cme_01_017-030 (2)
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[CONTRIBUTION
ROM THE
CHEMICALABORATORY
F
THE
OHIO
STATE NIVERSITY
THE
ME C HANI S M O F CARBOHYDRATE OXIDATION. XVII I.*
T H E O X ID A T IO N O F C E R T AI N S UGAR S W I T H S I L VE R OX I DE
I N T H E P R E SE N CE O F P OTAS SIUM H YD R OX I DE
K .
G.
A. BUSCH,
J.
W.
CLARK , L. B. GENUNG, E .
F.
SCHROEDER,
AND
W.
L. EVANS
Received February 16 1986
A
clearer un ders tand ing of t he m olecular reaction m echan ism involved
in the oxidation of various carbohydrates may be obtained through an
experimental stu dy of th e behavior of these im por tant com pounds towards
reagents that will yield oxidation products differing respectively both in
kind an d in number. Glucose m ay be oxidized completely by alkaline
potassium permanganate solutions' to carbon dioxide, and oxalic and
trace s of acetic acids, w hile w ith silver oxide und er the sam e conditions,
carb on dioxide, an d oxalic, glycolic, and fo rmic acids are t he final reaction
products. I n th e acid medium of copper ace tate solutions containing an
excess of this s alt, glucose m ay be oxidized to glucosone, carbon d ioxide,
and formic, oxalic, and glyoxylic acids? A comparative study of the
d at a ob taine d throu gh th e use of reagents3 of differing oxidation po tentia l
on the sugars and their various theoretical degradation and oxidation
interme diates seems to offer
a
fruitful meth od of a ttac k on this imp orta nt
oxidation problem.
The reagent chosen for the studies reported in this paper was silver
oxide, both alone and in the presence of added alkali . K i l i a ~ ~ i , ~ef,6
Behrend and DreyerlBDenis' an d Witzem ann* are among those who hav e
studied t he action of th is reagen t on various sugars an d their inter-
mediate degradation com pounds. Th e use of silver oxide in the stu dy
of carb ohy drat e oxidation offers certa in unique adv anta ges. T he oxi-
datio n pro ducts formed a re carbon dioxide, and oxalic, formic and glycolic
* C o n t r i b u t i o n XVII of this series,
J.
Am. Chem. SOC. 7, 200 (1935). T h i s
ar t ic le was submit ted in response to t he inv i ta t ion of th e edi tors.
EVANS
ND COLLABORATORS, J . Am. Chem. Soc. 47,
3085, 3098, 3102 (1925).
EVANS, ICOLL,T R O U S E
ND
WARINC,
bid . ,
60, 2543 (1928).
a K A R R E R
ND
PFAEHLER,elv. Chim. Acta 17, 363, 766 (1935).
KILIANI,
er.
13,2 703 (1880);
Ann.
206, 187, 191 (1880).
NEF, Ann. 367, 287 (1907).
B E H R E N D
ND
DREYER,
nn.
416,
203
(1918).
D E N I S ,Am. Chem.
J.
38, 578 (1907).
* WITZEMAN,
h.D. d isser ta tion , Th e Ohio Sta te Univers i ty ,
(1912).
1
TEE
JOURNAL
OF O R G A N I C
CHDb IBTEY,
VOL 1,
NO.
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2 BUSCH, CLARK, GENUNG, SCHROEDER, AND EV A N S
acids, all of which can be determined qua ntitativ ely. Th e silver remain-
ing after oxidation may be easily separated from the unchanged silver
oxide, and from its weight the oxygen consumed may be calculated.
Th e reaction is com paratively rapid and hence does not necessitate a long
tim e for its completion. Th e main objective of these experim ents was to
stu dy the behavior of mannose, fructose, arabinose and compo unds re-
lated to these carbohydrates towards silver oxide in the presence and
absenc e of alkalies un der carefully controlled conditions for the purp ose
of obtaining accu rate qua ntitati ve d at a which might shed more light on
the mechanism involved in the oxidation reaction.
EXPERIMENTAL
Reagents.-All t h e reage nts used in these experime nts were examined for the ir
pur ity b y th e usual well-known lab ora tory procedures.
Carbohydrates.-The carbo hyd rates used were of th e highest ob tai na ble pu ri ty .
Th eir iden ti t ies were verified b y determinations of thei r specific rotations, and by
oth er means when necessary.
Sil ver Oxide.-A so lu tio n of 400 g. of AgNOa in 1200 cc. of d ist ill ed wa te r was
vigorously s t i r red and a solution of 150 g. of KOH in 800 cc. of water was added a t
the ra te of 100 cc. per minute. Th e size of t he bat ch was later increased to as much
as 2000 g. of AgNOa bu t th e sam e conc entratio ns were always ma intaine d. T he
brown Ag,O th us precipitated was washed with wate r by decantation unti l the wash
wa ter was free of Ag+ an d a 100-cc. sample req uired less tha n
0 . 3
cc. of 0.1N HC1
to neutra l ize the a lka l i present. Th is usua l ly required abo ut ten washings .
T h e
AgzO was th en dried
at
110C. under vacuum. When dried a t this temperature, i t
was changed from th e chocolate-brown color of t he fresh ly precip itated oxide to a
dark purplish-brown.
If
dried a t 85 C., th e original brown color w as retained.
After drying, t he oxide was passed through
a
100-mesh sieve, placed in brown bot-
t les and s tored in the dar k .
It
was believed a t first th a t different lo ts of silv er oxide
would give s l ightly different results , but i t was later shown that when the above
directio ns were carefully followed, uniform re sul ts were always obtain ed. AgnO
was analyzed before using for total s i lver, ammonia-insoluble matter and carbon
dioxide. Th e analysis of th ree typical batches of the AgzO th us prepared an d
labeled (a), (b), and (c) was as follows: Silver, (a) 92.6%; (b) 92.20%; (c) 92.95%;
the ore tica l 93.1%: COz, (a) 0.10%; (b) 0.05%; (c)
0.03%:
Ammonia-insoluble, (a)
0.07%; (b) 0.09%; (c) 0.12%.
Ap paratu s and Analytical Procedures.-Seven gram s of silver oxide was adde d t o
100 cc. of 1.ON KOH conta ined in a 150-cc. carbo n dioxide flask, fitted with a s to pp er
carry ing a thermometer and a smal l s topcock. Th e flask was then p laced in the
the rm os ta t ma in ta ined
at 50
and th e reagent was al lowed t o come to tem pera ture ,
after which one four-hundredth of a mole of the sugar (e.g., 0.45 g. of mannose,
glucose,
or
fructose, o r 0.375 g. of arabinose) was added, the s top per was inserted
in the flask and the s topcock closed. By closing the s topcock after insert ing th e
stopper, an y pressure effect caused by forcing in the lat t er was prevented. When
this was done, i t was found unnecessary to wire on the s toppers to prevent them
being blown out , an d no loss of c arbo n dioxide was experienced. In th e experiments
carried ou t in th e absence of added alkali , the only change made i n the above pro-
cedures waS t h a t of us ing
11
g. of AgzO instead of
7,
an d carbon-dioxide-free wate r
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MECHANISM
OF
CARBOHYDRATE OXIDATION 3
was used in place of t h e
1.ON
a lka li . T he reac t ion mixtures were then agi ta ted by
a mechanical shak er during the various periods of t im e indicated in Fig. 1.
Th is technique was a t tended by a quick r ise in temp era ture wi th
a
m axi m um of 5,
which rapidly subs ided to the th ermo s ta t ic temp era ture .
Determination of Consumed Oxygen.-After th e reaction flasks were removed from
the th erm os ta t the y were cooled and the reac t ion mixture was decanted th rough a
previously weighed and dried Gooch crucible. T he silver-silver oxide mix ture re-
maining in the flask was washed several t imes by decantation and the fi l trate and
washings were mad e up to a volume of 250 cc. Th is solutio n was used for th e deter-
min ation of oxalic, formic, and glycolic acids. T o th e residue in th e flask was add ed
50 cc. of dilu te NH aO H
1:3)
nd th e flask was shaken vigorously to h asten solution
of the A g20 . Th e undissolved s i lver was allowed to sett le and the l iquid was de-
canted through the Gooch cruc ible . Th e ammoniacal solu t ion , thus obta ined, was
immedia te ly added to a beaker containing an excess of HC1 to prevent explosions
of the kin d reported b y previous workers .
Th e s i lver residue was washed wit h two more 50-cc. portions of th e NHaOH, th e
final washing being tested with HC1 to make certain that al l the s i lver oxide was
removed. Th e Ag residue was now transferred to th e Gooch crucible, washed w ith
wa ter, dried in a vacuum oven a t llOC., and weighed. T he oxygen consumed in
th e oxidation was calculated from the weight of s i lver thus obtained afte r correcting
for ammonia-insoluble impurit ies .
Cai-bon Dioxide.-The determ ination of carbo n dioxide was made on a second
sample obta ined in exac t ly the same manner as the sample used for th e de terminat ion
of the acids. T he flask was cooled t o
a
tem pera ture below 40C. as soon
as
it was
removed from the th ermo s ta t and was then connected to a carbon dioxide appa ra tu s
aThich was esse ntially t he sam e as t h a t described b y F o ~ l k . ~
O d i c Acid. -Oxal ic ac id was de termined by prec ip i ta ting as ca lc ium oxa la te
wi th ca lc ium ac e ta te in th e presence of ace t ic ac id and th en t i t ra t in g th e ca lc ium
oxala te wi th potass ium permanganate in the usua l manner. Th e calc ium conten t
was verified by conversion of th e oxalate t o th e sulfate .
Foiemic Acid.-T wo-fifth s of the fi l trate from th e oxidrtt ion mixture was placed in a
500-co. roun d-bo ttom flask fitted wit h
a
dropping funnel, capil lary tub e, andKjeldah1
bu lb . Th e l a t t e r was connected , w i th an adap te r , t o a spi ral w ater condenser, thee nd
of which exte nded t o th e bo tto m of a 500-cc. suction flask. Sufficient6.OMphosphoric
ac id was added bo th to neutra lize the a lka li present in the oxida t ion mixture and to
form the monopotassium salt . Th e suction flask was the n connected to a water pump
and the mixture was dis t i l led under vacuum, the round-bottom flask being placed
in
n
wa ter bath k ep t a t 50C. Two successive 50-cc. portions of water were added
and dis t i l lation was carried to dryness each t ime t o insure the presence of al l the
formic ac id in the d is t i lla te. Th e d is t i l la te was t i t ra te d f i rs t wi th s tan dard a lka li ,
using thymol blue as th e indicator, an d th en by t he Jones10011 method. Usually,
th e two de terminat ions gave very near ly the same result , bu t when the tem pera ture
a t which th e distillatio n was carrie d ou t was allowed t o rise above 55, or when
large amounts of glycolic acid were present, the permang anate value was sometimes
higher than th a t g iven by the a lka li t i t ra t i on . Th is was found to be due to the d is ti l -
lat io n of sma ll am ou nts of glycolic acid wi th th e formic acid. Ap prop riate correc-
t ions were made in each case.
9
FOULKSNotes on Qua nt i ta t ive
Analysis,
McGraw-Rill Book Co.,
1938,
p. 220.
1 0
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4
BUSCH
CLARE, GENUNG, SCHROEDER, AND
EVANS
Glycolic Acid.-The residue rem aining aft er th e formic acid distillation was
ti tr ate d for glycolic acid by th e Jones method. Any glycolic acid th at had dis t i l led
over wi th th e formic ac id was ca lcula ted and add ed to th a t found in th e residue.
This method leaves much to be desired, s ince i t is essential ly
a
determinat ion by
difference, but
a
search thro ugh the l i te ra ture fa i led to offer
a
better procedure.
An a t tem pt was made t o prec ip ita te g lycolic ac id wi th bas ic lead ace ta te , but t he
prec ip ita t ion was found to be quan t i ta t ive only wi th in
a
very narrow range of condi-
t ions which could not be duplica ted when us ing th e oxida t ion mixture . T ha t the
compound measured by difference was glycolic acid was proved by using larger
qua nti t ie s of t he sugar a nd isolating the pure acid, which was identified by the
method of mixed melting points.
THEORETICAL PART
When aqueous solutions of mannose, glucose, fructose, arabinose,
eryt hrito l, glyceraldehyde, or glyco laldehyd e are oxidized with silver
oxide in t he presence a nd absenc e of 1.0
N
K O H a t 50C., th e final reaction
products in each case are carbon dioxide and oxalic, formic and glycolic
acids. T he experimental da ta presented in this paper will be inter prete d,
as
in ot he r papers of thi s series, from t he sta nd po int of Nef's12 enediolic
conception of the chem ical behavior of th e carboh ydrates. His views
were founded on and are an extension of those of F i ~ c h e r , ' ~nd Wohl and
Neuberg14 con cern ing th e presence of hexose enediolic forms of the carbo-
hy dr ate s in alkaline solutions. Some of the recent work in this field, and
points
of
view having
a
bearing on this theory are herewith summarized.
T h e existence of th e enediolic functiona l group , -C(OH)=C(OH)-, is
now a n accepted fact, as is evidenced by th e following instances. (a) Fen-
obtained dihydroxym aleic acid by t he oxidation of tartari c acid.
(b) M ore recently its presence has been established in th e molecular struc-
ture of Z-ascorbic acid (vita mi n C) and related substa nce s. (c) T h e isola-
t ion by Eu le r and M a r t i d B f
Redukton
C3H403,rom a n aqueous alkaline
solution of glucose which had been hea ted t o
90
unde r a stream of nitro-
gen is a discovery of th e first im por tanc e in thi s connection. The se in-
vestigators regarded
Redukton
(11) as a n enediol of tar tro nic aldehyd e ( I).
It
should be noted that
Redukton
may be considered as the enediol of
hyd rox ym ethy l glyoxal (111), discovered b y Ev an s and Waring.17
It
was
late r isolated by N orris h an d Griffiths'7 in th e photoche mical decom-
position of methy l glyoxal. These workers also pointed o ut t h a t th e
14 NEF,
Ann.,
336, 191
(1904);
367, 214 1907); 76, (1910); 403, 204 (1913).
l
FISCHER,
Ber., 28, 1145
(1895).
14 WOHL
ND
NEUBERG,bid . , 33, 3095 1900).
' ENTON,
J
Chem.
Soc.
87,
804 1905).
15EULERND MARTIUS,Ann., 606, 73 (1933).
17
EVANS
ND
WARINQ, Am .
Chem.
SOC., 8,2678
1926).
17.
NORRISH
ND
GRIFFITHS,.C.S.
928,
28-29.
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MECHANISM OF CARBOHYDRATE OXIDATION 5
aqueous solutions
of
hydroxy pyruvic aldehyde must contain its tauto-
meric form, the t ar tronic aldehyde enediol. T he interrelationship of these
three compounds may be shown as follows:
CH O H C-OH CHzOH
C H O H e C-OH 2-0
I I I
II
CHO
1)
With reference to the chemical character of the hydrogen atoms in the
enediolic functional group, Euler and Martius found that
Redukton
pos-
sessej th e acid ity of a n organic acid of average stre ng th K
= 1 X
;
i.e., it is a little weaker than acetic acid K 1.8
X
Th us it is seen
that the enediolic functional group imparts polar properties to the carbo-
hydrate in which it is present.
Winters1*glucic acid, obtained from a so lution of inv ert sugar in lime
water, and also isolated b y N elson a nd Brownelg from a similar solution
of glucose (cerelose), was assigned th e molecular form ula, C3H403,by the
latteir investigators. Like Redukton it possessed strong reducing proper-
ties, and also absorbed iodine. It was thought by Nelson and Browne
to be hydroxyacrylic acid, CHO H= CH COOH . T he properties of
glucic acid and
Redukton
compounds possessing the same empirical
formula, are strikingly similar.
Fro m the ir determ ination of t he alkali-fixing cap acity of t he m ost im-
po rta nt sugars, the conclusion reached by Hirsh and Schlags,20 would
indicate th at these compounds are dibasic. Th e da ta obtained by Urban
and 13haffeF appea r to indicate t h a t w ith glucose, fructose and sucrose a
third acidic group begins to function at high alkalinity; but because of
large errors in this region the existence of th e third gro up mus t be regarded
as uncertain.
Nef2 postulated furthermore th a t th e carbo hydrate enediols in alkaline
solutions would undergo scission
at
the double bond, thus yielding frag-
me nts containin g a bivalent c arbon atom , a typ e of compoun d whose exis-
tence was one of t h e cent ral ideas in his theo ry of o rganic chemical be-
havior.
If
these fragm ents were formed in th e presence of oxidizing agents,
they were oxidized to the corresponding acid, or to compounds having a
smaller num ber of carbon atoms tha n the fragments themselves. I n the
* a WINTER, 2.Ver . Rubenzucker Znd. 44 old series ,
1049 1894).
1s
NELSON
ND BROWNI E,.
Am. Chem.
SOC. , 1, 30 (1929).
20 HIRSH
AND SCHLAGS,.physik. Chem. 141, 387 1929).
2 1
URBAN N D SHAFFER, Biol. Chem. 94,697
1931-32).
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6 BUSCH, CLARK, GENUNG,
SCHROEDER, AND EVANS
abse nce of oxidizing agen ts, i.e. in the presence of alkalies,
a
scission of the
carboh ydrates would ta ke place, giving rise to fragm ents containing
a
smaller numb er of carbon atoms tha n th e original carboh ydrate.
This
has been am ply evidenced in the lite ratur e of this field.
Saccharinic acids
of th e original carb oh ydra te or of it s fragm ents m ay form , a reaction which
has be en experimentally investigated by Kiliani,*2NefI2, Shaffer an d Friede-
mann.23
T he postulate concerning the fragm entation of C=C has met with very
definite objections. (a) Such
a
reaction is not in accord with Schmidtsz4
rule which states that the fragmentation takes place at the C-C in the
CY-@
position to the
C=C.
It should be pointed out that the data upon
which this generalization rests were obtained under much more drastic
experimental conditions than have been employed in alkaline solutions of
the carboh ydrates. T he enediolic group is a polar one and is very reac-
tive even a t ordinary temp erature. (b) T he relative values of the well-
know n bond energies would fav or fragm entation
at
the
C-C
rather than
a t C=C.
Hirst25 an d his collaborators have shown t ha t with th e usual reaction
involving ozonization and subsequent hydrolysis, tetramethylascorbic
acid will give 3,4-dimethylthreonic an d oxalic acids. Fento n15 found
th at dihydroxymaleic dime thyl ester was decomposed in dilute am monium
hydroxide with the formation of oxam ide. H e suggested th at t he ester
had ruptured
at
the double bond.
If
it is assum ed th a t alkaline solutions of re ducing sugars con tain
enediolic forms, it w ould seem t ha t the mechanism involving
a
scission at
the double bond in the presence of alkalies and also th at takin g place in th e
presence of alkaline oxidizing agen ts would necessitate one of two poin ts
of view;
z.,
(a) either
a
scission of th e enediolic gro up followed b y ox ida-
tion, i. e. Ne fs view, or (b ) a different mec hanism of ru pt ur e in the presence
of alkalies alone, an d still ano ther m echan ism for alkaline oxidation in which
oxygen plays a pa rt, such as th e oxidation of ascorbic acid referred to above.
Among th e concepts which migh t offer a simple pictu re of th e me chanism
involved in the scission of
C=C
are those suggested by the electronic
theory,26 nd one outl ined by D r. C. L. Bernier of t his La bo rat ory which
involves
a
simple combination of th e enediol theory and a reverse aldol
condensation.
22 Cf. TOLLENS,Handbuch der Kohlenhydrate, 3 Auflage, 1914,
pp.
778-779.
23
SHAFFER
ND FRIEDEMANN,
.
Biol . Chem., 86,
345 (1930).
24 SCHMIDT,hem. Rev. 7, 137 (1935); Ber.,
68,
60, 795 (1935); Cf. Neuberg,
25
HIRST
ND COLLABORATORS, J SOC. hem. Ind. ,
62, 221, 1270 (1933).
20
Cf.
STIEGLITZ,
roc. Znst. Medic ine
of
Chicago,
1, 41 (1916);
Chem. Abstr., 17,
ibid,
505.
3878 (1923).
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MECHANISM O F CARBOHYDRATE OXIDATION 7
The following discussion is concerned primarily with the sources of the
four ireaction produc ts found i n these studies, an d th e ex ten t of fragm en-
tati on which occurs in mannose a nd fructose under th e experimental con-
ditions used.
Mtsnnose
an d Arabinose.-When a n aldohexose like manno se is acted
upon b y a n alkali it m ay undergo th e kind of chang e indicated in th e fol-
1owin.g reaction :
H O
H
CHO CHOH
\ /
I
II
I
C-OH
I
310-C-H HO-C-H
e
0-A-H H0-C-H
H-C-OH H-L-OH
(1)
HO-C-H?l
I
I
H- SOH
H-C-OH H-C-OH
CHzOH
I
I
H-C
I
CHZOH
HzOH
(d-man nose) (aldo-d-mannose) (d-mannose, 1,2-enediol)
A
fragmentation of the mannose 1,a-enediol between carbon atoms 1 a n d
2
would yield one molecule of arabinose a n d one of formaldehyde,
L e .
CHOH
I
-C-OH
II
C-OH
I
HO-C-H
4
t
I
I
I
H-C-OH
OH
\ /
/ \
C
H
H-C-OH H-C-OH
CHZOH
I
CHzOH
(d-mannose, 1,L- ened iol) (d-arabinose,)27 (formaldehyde,)*'
active f o r m ac t ive
form
T he form aldehyde molecule thu s formed would b e oxidized to formic a cid.
It is clear that the arabinose molecule in alkaline solution may in turn
undergo the same kind of fragmentation as does mannose, until finally
five molecules of formic acid would be formed from th e original pentose,
provided, however, that it reacts in only one direction.
As
set forth in
Fig. 1, th e results of o ur experiments show th a t hexoses, such as glucose
27 BALY,
Rice
Znst. Pamphlet,
12, 93
(1925).
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8
BUSCH, CLARK, OENUNO,
SCHROEDER,
AND E V A N S
an d galac tose, are oxidized b y silver oxide in th e absence of potassium
hydroxide to carbon dioxide, and oxalic, glycolic and formic acids, and
th at the ultimate fate of the o xidation produ cts formed is conversion to
carbon dioxide. I n the presence of added alkali, the salts thu s formed
tend to become stable tow ards silver oxide, a fact w hich confirms Witze-
manns observations in this respect with reference to potassium formate,
a substance which he found to undergo oxidation slowly when heated.
Ou r experimen tal da ta show th a t d-glucose in th e presence of silver
oxide and potassium hydroxide reached a maximum production of formic
acid a t the end of one hour
ie.,
1.5 moles per mole of sug ar), ma nnose
Percentage of Carbon Returned from d-Galactose
9ZW 9241 98.75
99.M
4:
ii
k 4
. y
t i j a g
ZG
; :
b o
2
s 20
3 ~
- - L
4 8 I2 2 24
H o u r s
A t o m s o f Oxygen p e r
Mole
of
d-Glucose
Atoms of
Oxygen
per Mo le
o f
d-Galactose
z4
Consumed 267564 11.75
Calculated
850 fl.10 12.0
Consumed
928 11.75
IbS I/.
Culculated d Y 11.22
Il
66 fm
FIG.
1
2.74
moles in
24
hours, galactose
2.42
moles in
12
hours and fructose
3.1
moles in 24 hours. Th e significance of these d at a lies in the fact th a t in
order t o p roduce yields of formic acid in excess of 1mole as demanded b y
equation (2)) either the original hexose must undergo a fragmentation
between carbon atoms 2 and 3 to give glycolaldehyde and erythrose, be-
tween carbon atoms 3 and 4 to give two molecules of glyceralde hyde, or
the pentose formed in the fragmentation between carbon atoms 1 and 2
mu st suffer a further degradation in the m anner just ou tlined for a hexose.
Tha t the
first
ste p in the frag men tation of the d-mannose molecule under
our exp erimen tal conditions would seem to be th e formation of arabinose
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MECHANISM OF CARBOHYDRATE OXIDATION 9
and formaldehyde [equation
(2)]
follows from an examination of the data
obtained a t th e end of four hou rs, at which time th e total carbon returned
in eac h case is
99.45
per cent for arabinose and 99.33 per ce nt for mannose.
If the mannose molecule, on fragmentation, yields one molecule of
form alde hyd e an d one of a rabinose per mole equivalen t of sug ar used,
TABLE I
DATA.XPRESSEDS MOLES ER GRAM-MOLEQUIVALENT
F
CARBOHYDRATESED
OXIDATION
PRODUCTS
Oxalic Acid
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Formic Acid . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Glycolic Acid. .
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Carbon Dioxid e.
. . . . . . . . . . . . . . . . . . . . . . . . . . .
Atoms Oxygen Consumed, . . . . . . . . . . . . . . . . . .
MANNOSE
0.98
2.69
0 .56
0.19
6.69
A R A B IN O S E
0.89
1.64
0.71
0.13
5.46
DIFFERENCES
+0.09
+1.05
-0.15
+0.06
+1.20
Oxidation
of
Aqueous Solutions (a025
Malar of
d-Mannose
and I-Arabinose
wi th
S i l v e r
Oxide a n d 1.0N. Alkal i at 50C.
Percentage
o f
Carbon Returned from I-Arabinose
95zo 99.45 99.40 IOL80
Percentage of
Carbon Returned
from d-Mannose
U
.--Form/cAcid
Id-Maywse
f ,
97.67
99.33
97.17
96.63
B Y e
4 8 I2
: I6
20 24
Carbon
Dioxide
(d-Mannose)*
Ours
.Carbon Dioxide(L-Arabinw)
A t o m s of
Oxygen
per Mo le of & M a n n o s e
Consumed
630
669 6.95 7:N
Calculated
hJ4
656
6.66
k.
78
Atoms o f Oxygen
per Mole o f
Z-Arab inose
Consumed
528
X46
549 S 8
Calculated 509 529 5 5 6 9
FIQ.
the n it is clear th at the yields of formic acid from these two c arboh ydrates
should differ by
1.0
mole, and the yields
of
carbon dioxide, and glycolic
and oxalic acids should be the same from both sugars. Th e data in Table
I
show th at these assumptions are approximately tru e in this case. Hence,
it may be safely concluded that d-mannose (0.025 molar solution) is de-
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BUSCH, CL ARK, GE NUNG, SCHROEDER, AND E V A N S
O X I D A T I O N P R O D U C T S
Carbon
D i o x i d e . . . . . . . . . . . . . . . . . . . . . . . . . . .
Oxalic Acid. .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Formic Acid
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Glycolic Acid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
graded approximately into formaldehyde and arabinose as the first step
in its oxidation with silver oxide in the presence of 1.0
N
alkali at 50C.
P. Fleury and J. Lang e2* btained one mole of fo rmald ehyd e by the oxida-
tio n of glucose with periodic acid , which K arr er an d Pfaehler, loc. c i t . )
ascribe to
a
rupture of glucopyranoside between carbon atoms 5 and 6.
T he complete da ta over a period of 24 hours are shown in Fig. 2.
T he fa te of th e arabinose molecule from mannose can be fairly well
understood b y a comparative stu dy of it s oxidation da ta obtain ed after
24 hours with those from erythritol, a compound which we had to use
instead of t he ra re suga r erythrose, a t this writing know n only as a sirup.
These are shown in the following table.
A R A B I N O S E
0.180
1.010
1.690
0 . 6 0
TABLE
I1
DATA XPRESSED
S
MOLES
ER
GRAM-MOLEQUIVALENTSED
O X I D A T I O N P R O D U C T S
Carbon
Dioxide. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Oxalic Acid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Formic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Glycol ic Ac id . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
T W O
MOLES
E ~ ~ ~ H ~ ~ ~ c
LYCOLALDE- DIFFERENCES
H Y D E
0 .124 0 .092
f O ,032
0 .594 0 .648 -0 .054
1.045 1.174 -0.035
0 .803 0 .720
0.08
E R Y T R R I T O L
0 .124
0 .594
1 .045
0.803
D I F F E R E N C E S
0.064
$0.416
0.645
-0 .203
From the differences in the yields of formic and oxalic acids it is clear
that the arabinose is not being fragmented into formaldehyde and ery-
throse,
a
condition which would cause a difference in th e yields of fo rmic
acid of one mole per mole
of
arabinose used. Previous work has shown
t h a t
a
tetr os e sugar ten ds to give two molecules of glycolaldehyde instead
of one each of glyceraldehyde and formaldehyde. If this is so, it is con-
ceivable th at th e erythrose formed from a fragm entation of arabin ose
might yield oxidation data approximately the same as that for two mole-
cules of glycol aldehy de. Since we do no t know th e conce ntration of th e
erythrose in this reaction, th e d at a used can be assumed to show merely
~ ~ F L E V R Y
ND
LANGE, . pharm. chim.,
8 ]
17, 1 (1933); Chem. Abstr .
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MECHANISM OF CARBOHYDRATE OXIDATION
11
th e tendency of th e reaction. Such da ta are given for eryt hrito l an d
glycolaldehyde after twenty-four hou rs in Tab le
111.
T he d at a for glycol-
aldehyde are two-thirds of those obtaine d from a thr ee molar solution, an d
are used only as an approximation.
Glucose.-Under ou r experim ental conditions glucose an d arabinose do
not show the same simple relationship with reference to formic acid yields
which seems to exist between mannose and arabinose, as is evidenced by
the fact that at the end of one hour glucose yielded 1.5 moles of formic
O x i d a t i o n o f Aqueous
Solutions
of
d-Glucose (0.025 Molar) and dl-Glyceric Aldehyde (0.050 Molar)
with Silver
Oxide a n d 1.0
N. Alkal i
a t
50C.
Percentage
of
Carbon Returned f r om dZ-GlycericAldehyde
96.36
96.72
97.11
OJ Percentage o f Carbon
Returned f rom d-Glucose
r 98.00 9650 9833 96.50
-5
5 2
0 .u_
u l i
= J 3
E 8
G g
% I
=2
._
z k
0
k
w e
2
0
1
9
Hours
-
4
8
/Z
/6
20 24
Atoms of
Oxygen per
Mole o f d-Glucose
C o n s u m e d 718
iT40 253
i If
Caliculated
6.7/
6.70
728
232
C o T s u m e d
552
566
24
Calculated 562 584 AM
FIQ.
A t o m s
o f Oxygen
per
TWO
Moles of dl Glyceric
Aldehyde
acid, and arabinose 1.55 moles per mole equiva lent of c arb oh yd rate used.
Fig. 3
is
a graphic comparison of the data obtained from glucose with
those which would have been obtained had this hexose molecule undergone
cleavage in to tw o molecules of glyceraldehyde. It is evident from these
experimental results that glucose reacts in more than one direction.
T h e formation of oxalic acid from glucose, manno se, galactose, arabinose,
fructose, glyceraldehyde and similar compounds may arise from the for-
mation of an a-keto-acid
of
th e hexose as well as
of
the other theoretically
possible keto-acids of fewer carbon atoms. T he keto-acid m ay enolize an d
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12
BUSCH, CLARK, GENUNG, SCHROEDER, AND EVANS
then undergo a fragm entation, th us yielding glyoxylic acid, which in tu rn
is oxidized to oxalic acid, in accordance with the following reaction.
R
R
R
CH O H --&-OH >(O H) .corn
C-OH
I
(3)
co
- -OH
I I
+
l + o
COOH
COOH
COOH
OOH
Fructose:
Glycolic
Acid.-The most plausible source of glycolic acid is
glycolaldehyde. Fro m our studies we are led to believe th at t he primary
alcohol group in the sugars studied is only slowly attacked under our
conditions and it appears in the oxidation products chiefly as glycolic
acid. On th e oth er han d the secondary alcohol groups are rapidly oxidized.
Our experiments show that ethylene glycol is stable towards silver oxide
and alkalies while glycerol is most readily attac ked . Ta ble
I V
shows the
T A B L E
I V
M OLESOF GLYCOLIC CID FORMEDER M OLE O F COM POUNDXIDIZED
&Glucose . . . . . . . . . . 0.70 &Mannose. . . . . . . . . ..0.75 &Galac tose . . . . . . . . ..0.76
d-Fruc tose . .
. . . . . . . . 1.09 d-Arabinose. . . . . . . . .
0.81
&Xylose . , . . . . . . . . . . 0 . 4 5
Ery th r i to l .
. . . . . . . . .
.1.18 dl-Glyceraldehyde.. . 0 . 5 7 Glycolaldehyde.
. . . .
O . 52
nu mbe r of moles of glycolic acid form ed per mole of com pou nd oxidized
after th e reaction has proceede d for one hour a t 50 . Since the glycolic
acid obtained from the aldo-sugars tends to approach, but never exceed,
one mole per mole of com poun d used, and t h at from fructose an d ery-
thritol does exceed one mole, the glycolic acid can be easily accounted for
on th e basis of glycolaldehyde form ation arising in each case from t he
primary alcohol group and its neighboring carbon atom, formed by the
fragmentation of the sugar at th at point. T he forma tion of
2 ,3 -
and
3
,
-enediols would furnish additional primary alcohol groups in the aldo-
sugars a nd hen ce should furn ish more th an one mole of glycolic acid per
mole of sugar used. Fro m the da ta tabu lated it
is
seen that this does not
take place under o ur experimental conditions. Dr. Charles L. Bernier of
this laboratory has shown that d-glucose in aqueous potassium hydroxide
solutions a t 50 will yield 51.19% of lactic acid , th e for eru nn er of which
m u st be g l y ~e r a l d e h y d e .~ ~
I n view of th e da ta obtaine d with fructose and er ythr itol, and m ore
especially th e probab le fac ts with reference to glycolic acid form ation giv en
20 WEISENHEIMER, er., 41, 1009 (1908).
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MECHANISM OF CARBOHYDRATE OXIDATION 13
QLYCOL-
A L D E H Y D E
0.046
0 .324
0.590
0 . 3 6
above, it may be assumed that it is th e keto-hexose which will undergo
a
fragmentation to give erythrose and glycolaldehyde according to the fol-
lowing equation :
HO CHzOH CHzOH CHzOH
C-OH
C-OH CHzOH -C-OH
H-C-OH
H-C-OH
CHzOH
2,a-enediol) hyde, activ e activ e form)
I
I
I
I
bo
H--C:-oH o H - L H H-C-OH A
\ /
I
I
c
HO-( &-H HO-CH
I - + I
C-OH+ I
H-( --OH H- c -OH H-C-OH
CHzOH
I
CHZOHHZ
(d-f ructose) (d-keto-fructose) (d-fructose (glycolalde- (erythrose,
form)
That this fragmentation
of
th e fructose molecule probably does take place
under these experimental conditions seems to be borne out by the data
obtained from erythritol and th at obtained by using one-third of the values
BUM FRUCTOSE
. 1 7 0 0 . 1 8
0 . 9 1 8 0 . 8 5
1 .635 1 .77
1 . 1 6 3 1 . 1 7
TABLE
V
Carbon
Dioxide.
. . . . . . . . . . . . . . . . .
Oxal ic Ac id . . . . . . . . . . . . . . . . . . . . . .
Formic Acid . . . . . . . . . . . . . . . . . . . . .
Glycolic Ac id . . . . . . . . . . . . . . . . . . . .
OXIDATIONRODUCTSN MOLESPER
O X I D A T I O N P R O D U C T 8 E R Y T H R I T O I
0 .124
0 , 5 9 4
1 .045
0 .803
I
MOLE O F SUBSTANCE XIDIZED
DIFFEREWCB
-0 .010
+0.068
-0 .135
-0.007
TABLE
VI
OXYGENCONSUMPTION-MOLES
E R
MOLEOF SUBSTANCE XIDIZED
I
Oxygen, Used
. . . . . . . . . . . . . . . . . . . . .
5 .07
2 . 0 5 7 . 1 2
6 . 1 2 6 . 1 0
Oxygen, Calc'd . . . . . . . . . . . . . . . . . . . 4 . 8 8
2 . 0 1 6 . 8 9
5 . 8 9 5 . 8 6
from glycolaldehyde oxidation as a n app roximation to th e da ta which we
would ha ve obta ined had we had sufficient glycolald ehyde for all our ex-
perim ental purposes. If the keto-hexose undergoes fragmentation in this
manner the sum
of
the products obtained from the tetra-hydric alcohol
and .the glycolaldehyde should be approximately equal in value to those
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BUSCH, CLARK, GENUNG, SCHROEDER, AND EVANS
0.18
0.85
1 . 7 7
1 .17
6.10
obtained with fructose. T ha t this is approximately
so
under the experi-
mental conditions used
is
seen from Table
V.
Th e tetrose formed in this
reaction is believed t o fra gm en t into two m ore m olecules of glycolaldehyde.
0.04
o. 12
0.00
-0.09
f 0 . 0 5
TABLE VI 1
COMPARISON
F
OXIDATIONATA
OR
FRUCTOSEONE
MOLE)AND
GLYCOL-
A L D E H Y D E
(THREE
OLES)
O X I D A T I O N P R O D U C T S
Carbon
Dioxide.
. . . . . . . . . . . . . . . . . . . . . . . . . . .
Oxalic Acid.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Formic Ac id . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Glycolic Acid. .
............................
Oxygen Consumed. .
. . . . . . . . . . . . . . . . . . . . . . . .
0.14
0 . 9 7
1 . 7 7
1 . 0 8
6 . 1 5
Oxidaf ion
o f
Aqueous
Solutions
o f
d -
Fructrose (0.025 Molar)
and Glycol
Aldehyde (0.075 Molar)
with
Si lver Oxide
and
1.0N Alkali
a t
5 0 O C .
P e r c e n t a g e o f Carbon Returned from Glycol Aldehyde
4g7l
/&2W
Im07
d
2 r I
P e r c e n t a g e
o f
Carbon Returned f rom
d-Fructrose
= 9967 96100 D O a9
99B
- t /E
I I I I
-
2
6 8
I2 16
20
24
s
Hours
Atoms
of
Oxygen p e r Mole
of
d-Fructrose
Consumed 107 5.55 5 1 6.ID
Calculated 485 419 548 5: 6
Calculated
4.98
5.49 603
FIQ.4
Atoms of
O x y g e n
pe r Three Moles
of Glycol
A l d e h y d e
Consumed
4.98
549
6.G
(See Table
IV.)
The oxygen relations at this point (Table VI) are of
equal interest in th is connection.
W hen the da ta obtained with fructose at the end of 24 hours are com-
pared with those obtained from
a
three mole equivalent of glycolaldehyde
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MECHANISM O F CARBOHYDRATE OXIDATION 15
under the same conditions, the differences are sufficiently small to justify
th e belief th a t fructose is oxidized to i ts final products indicated in T able
YII , by way of a n erythrose
+
glycolaldehyde stage, the erythrose thus
formed th en yielding two mo re molecules of glycolaldehyde-the to ta l
oxidation being, in effect, equivalent to oxidation of three molecules of
glyco [aldehyde. T h e complete experimental d at a for these oxidations
are giraphically shown in Fig. 4.
Carbon
Dioxide.-An exam ination of the graphica l da ta will show t h a t
th e yields of carb on dioxide were uniform ly low thr ou gh ou t th is series of
experiments, much to our surprise. Among th e possible sources of carbon
dioxide are potassium formate, glycolaldehyde, and any possible keto-
acids formed as oxidation pro ducts in th e course of t he reaction.
I n a sep arate experiment w ith glycolic acid
(0.57
g.) only 0.29% of the
carbon was conv erted to carbon dioxide. At the end of twenty-four hou rs,
a
three molar solution of glycolaldehyde 0.75 molar) gave
2.3%
of its
carbon a s carb on dioxide. Since we had no available keto-acid we oxi-
dized galactonic lactone because, as has been show n, the seco ndary alcohol
TABLE
VI11
OXIDATION RODUCTS
F
GALACTOSEN D GALACTONICACTONE
QLYCOLIC
ACID
Galactose.
.
.
.
. .
.
. .
.
. . .
.
. . . .
. .
. . . . .
Galac tonic L actone , . .
.
. . . .
.
. .
.
.
.
.
CARBON
DIOXIDE
0 . 3 5
0 . 3 4
OXALIC
ACID
1 . 4 4
1 . 6 6
FORM IC
ACID
2 . 1 5
1 . 79
0 . 3 2
0 . 2 3
group is readily at ta ck ed with silver oxide in the presence of potassium
hydroxide. I ts da ta are compared a t this point with those of galactose
a t t he end of
24
hours, the results in each case being in moles per mole of
compound used (Table VIII). It would seem that the chief sources of
th e carbon dioxide in these experiments are th e possible keto-acids formed
as intermediate oxidation produc ts, a n d the slow oxidation of glycolic and
formic acids.
SUMMARY
1. Glucose, mannose, galactose, and fructose have been oxidized in
.025 molar solutions with silver oxide in the presence of
1.0 N
potassium
hydroxide. T he ultim ate products in each case were carbon dioxide a nd
oxalic, formic and glycolic acids.
2 . Through a similar study of a number of the available theoretically
possible intermediate degradation compounds light has been shed upon
th e oxidation mechanisms of th e abo ve hexoses. T he following intermedi-
ates have been studied in this connection: arabinose, erythritol (for
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16
BUSCH,
CLARK, GENUNG, SCHROEDER, AND EVANS
erythrose), glyceraldehyde, glycolaldehyde, galactonic lactone (for a keto-
acid). I n all these cases the ultim ate products were the same as those
obtained with the hexoses.
3.
Th e first stage in th e oxidation m echanism of mannose seems to be
th e fragm enta tion of this hexose into on e molecule each of fo rmald ehyde
and arabinose, since its oxidation d at a differ from those of th e pentose by
appro xima tely one mole of form ic acid.
4.
Th e & st stage in the oxidation m echanism of fructose seems to be
th e fra gm enta tion of thi s hexose int o eithe r one molecule each of glycol-
aldehy de an d eryth rose , or int o thre e molecules of glycolaldehyde, since
the quantitative data obtained from the fragments in the two cases are
practically the same as that obtained from the keto-hexose.
5 .
Th e behavior of glucose is best understood on t he assum ption th at
it undergoes oxidation in more t ha n one direction.
6 . Th e formaldehyde obtained in the fragm entation of these sugars and
related compounds is th e source of th e oxidation p rodu ct form ic acid.
We have indicated that oxalic acid and the chief portion of the carbon
dioxide is derived from the fragmentation and subsequent oxidation of
keto-acids. Evidence is given for th e general stabil ity of th e primary
alcohol group towards th e oxidation m edium ; hence th e presence of this
group as glycolic acid in the final reaction products.
top related