IV.-On the Constitution of Lactic Acid. BY DR. H. KOLBE. THErecent experiments of Messrs. Perkin and Duppa* on the action of ammonia on bromacetic acid having verified the opinion long ago put forth by many Chemists that glycocol stands to acetic acid in the same relation as amidobenzoic acid HO.C, {g:NlC,O,,O tobenzoic acid HO(C,2H,)C202,0 it follows that glycocol may be regarded as amidacetic acid HO. C (giN)C,O,,O just as Cahours has shown? that alanine has the composition of amidopropionic acid HO.C {giN)C20,,0 and leucine of amidocaproic acid HO.C, -fHIO C202,O. @,r\T) These several amidated acids resemble each other in many respects and particularly in this ;-that when their aqueous (not alcoholic) solutions are treated with nitrous acid,- they yield a new series of acids free from nitrogen related to one another in the same manner as the amidated acids are among themselves but dis- tinguished from the latter by the substitution of 1atom of hydrogen and 2 atoms of oxygen,-that is to say of the elements of peroxide of hydrogen,-for the amidogen decomposed by the nitrous acid.From these and other considerations it may be inferred that the so-called glycollic lactic and leucic acids are analogous in chemical constitution to Gerland’s oxybenzoic acid and bear the same relation to acetic propionic and caproic acids that oxybenzoic acid bears to benzoic acid. From these relations and from a careful consideration of thc entire chemical behaviour of oxybenzoic glycollic lactic and leucic acids I have come to the conclusion that these acids are simple substitution-products of the primary acids benzoic acetic propionic and caproic and are derived from them by the sub-stitution of a molecule of peroxide of hydrogen HO, for one atom of hydrogen thus-* Chem SOC.Qu. J. xi 22. + Ann. Ch. Phnrni. cviii 106. olycollic acid is oxaretic acicl HU.(C -I H )c,o,,o ; CHO Lactic acid is oxypropionic acid HQ.( (1 {;~l)C,O,,O ; Leucic acid is oxycaproic acid HO.( c, ~:@,o,,o ; and the compositioii of oxybenzoic acid is expressed by the rational formula HO.( C, (~@,O,?O. The relations between the above-mentioned primary acids and the amidated acids and oxyacids derived from them will perhaps be made clearer by the following tabular view HO.(C2HaW2OpO HO.(C2 { 22N)C20& HO. (c2 { c20210 Acetic acid. Amidacetic acid (glycocol). Oxyacetic (glycollic) acid. HO.(C,H,K&O2,0 HO (C { :”> C20,,0 HO. (C2 { H4 ) C202,0HO2 Propionic acid. Amidopropionic acid (nlanine). Oxypropionic (lactic) acid. HO.(C,,H,,)C,02,0 H 0( Clo{ g:pN) C20,,0 KO.(C,,{ :5Jc20290 H0.(C14H6)C202,0 Caproic acid HO. (C, { EiN )C202,0 dmidocaproic acid (leucine). HO. (%{ Zoo,)C202~0. Oxycaproic (leucic) acid. Benzoic acid Oxybenzoic acid. The idea that peroxide of hydrogen can play the part of an elementary body and replace the hydrogen in an organic radicle appears at first sight so paradoxical and improbable that I was at first inclined to reject it; and it is only after long and mature reflection that I have been able to convince myself of its validity.The history of modern chemistry furnishes numerous instances of the ultimate adoption of hypotheses which at first appeared as improbable and paradoxical as the above,-for example the replacement of hydrogen in organic radicles by chlorine and even by peroxide of nitrogen;-and I therefore think it probable that the preceding hypothesis respecting the constitution of oxybenzoic acid may some day meet with less opposition than it is likely to encounter at present. To decide the question whether glycollic and lactic acid ought really to hc regarded as derivatives of acetic and propionic acids CONSTTTUTIOX OF LACTIC ACID. 17 it is necessary to ascertain whether the Gr&-mcntioned acids can be directly produced from and reconverted into the second I am at present engaged with experiments bearing upon this point and have already obtained by the electrolysis of acetic acid mixccl with sulphuric acid an acid which I believe to be oq-acetic acid.The inverse transformation tdres place so easily and coni-pletely,-as shown by U lrich (see the next paper),-tliat lactic acid will probably be found the best material for preparing large quantities of chemically pure propionic acid; and there is 110 doubt that oxyacetic and osycaproic acid may iu like manner bc easily converted into acetic and caproic acid. The preceding views are apparently incoiisistent with Wizr t z’s recent statement? respecting the behaviour of lactic acid with yentachloride of phosphorus and the products of decomposition of the resulting compound called by Wu r t z chloride of Zuciyl.From these facts indeed W ur t z has drawn conclusions totally different from the above and has in particular endeavoured to show that lactic (with 6 atoms of carbon) is a hibasic acid 2HO. (C6H402)0,. But ,the very facts vhich Wurtz brings forward in support of this view appear to me to prove ths correctness of nip own hypothesis on the constitution of lactic acid; indeed a single perusal of Wurtz’s memoir sufficed to convince me that his chloride of lactyl C6H,02,C3 is in reality the chloridc~ of chlorpropimy! (C4(Ef) C202,C1 (Iiomologous with chloridc of chloraceton~-~,(C2-fFf)C,02,Cl) ziid that tlie transfor-mation of lactic acid intb this compound by treating its lime-saIt with pentachloride of phosphorus takes place as represented by the equation Lactate of lime.Chloride of chloropropioxyl. + 2PO,C1 + CaCl 4-HC1; further that JT ur t z’s chlorolactic ether is chloropropionate of ethyl C,HS0.(C4 {$)C20,,0 produced according to the equation ~ * Ann C‘h. Z’hwni. cvii 194. VOL. XTI. C ( C {~i)c~o~,cl + C,II~O.HO = c,H,o.(c,(~)c,o,,o Chloride of chlorpropioxyl. Chloropropionate of ethyl. + HC1; and that it will be easy from these compounds to produce propionic acid itself. The experimental investigation of these questions has heen undertaken by Dr Ulrich who has shown that the product of the action of pentachloride of phosphorus on lactate of lime is 1 eally thc chloridc of cliloropropioxyl ; that this compound is converted by water into chloropropionic acid ; that Wurt z’ s chlorolactic ether is chloropropionate of ethyl ; and that either of these compounds when subjected to the action of water and nascent hydrogen easily reproduces propionic acid (see tlic following memoir).I therefore regard it as certain that lactic acid contains 6 atoms of carbon,-not 12 atoms as some chemists suppose,-and that it is monobasic and a derivative of propionic acid from which indeed it differs only by the replacement of one atom of hydrogen in the radicle by peroxide of hydrogen. Wvrtz has made the interesting observation that the so-called glycols liydrated oxidc of ethylene ‘231 C20,.2H0 hydrated oxide of propylcce ‘4’’5’ C202.2H0 ad liydi*ated oxide of HJ amylene ‘8‘’9? 11 J C20,.2H0 are converted by oxidation into oxy-acids viz, oxyacetic oxgpropionic and oxyvaleiic (butylactic) acid 110.(C {z60,)C,O2,0 respectively and hence concludes* that the glycols are the alcohols corresponding to theacids of the lactic acid series.In another paper,? which appeared a few months earlier Wurtz puts forth the opinion that oxalic acid is the acid corresponding to hydrated oxide of ethylene his words being as follows Bibasic oxalic acid may therefore be regarded as standing to the bi-acid compound gljcol in the same relation as acetic acid to ordinary alcohol,”-a view likewise entertained by other chemists. I regard both these views as decidedly false.The notion that glycols should be classed among alcohols is quite unfounded. However useful it may be to regard a number of heterogeneous * Ann. Cli. Phsrui. cvii 199. .F Ann. Ch. Pharm. ciii 368. CONSTITUTION OF LAOTIC ACID phenomena from one general point of view the attempt to extend the idea of an alcohol BO far 8s to include the so-called glycols is totally destitute of scientific value ; indeed by this unnecessary generalisation we rather incur the danger of losing altogether the definite conception of an alcohol. We have hitherto included in the class of alcohols the hydrated oxides of monatomic radiclee which besides many other general characters resemble each other especially in thie reepect that under the influence of oxidising agents they take up an atom of oxygen in place of an atom of hydrogen at the same time giving up their atom of basic water and are converted into aldehydes,- and subsequently by taking up two more atoms of oxygen into the corresponding acids.Now the first of these properties via. the power of generating aldehydes by oxidation is altogether wanting to the glycols For independently of the fact that no aldehyde has yet been prepared from either of the said so-called glycols it may be shown h priori by comparison of the rational formulae of ethyl-alcohol C,H,l C,O.HO and hydrated oxide of ethylene H (ethyl-glycol) ‘SE31 C20,.2H0 that the latter cannot like the former be converted into an aldehyde by oxidation. If in hydrated oxide of ethylene 1atom of hydrogen be converted into water and replaced by 1atom of oxygen-that is to say-if the compound be subjected to a process of oxidation analogous to that by which alcohol is converted into aldehyde the product must evidently be not an aldehyde but a body having the composition of acetic acid : c2E3) C20,,2H0 + 20 = (C,H3)C20 + 3330 this product will in fact either be hydrated acetic acid or a 1)ody homologous with hydrated oxide of lipyl (C,H,) C,,03.3H0 viz.hydrated teroxide of acetyl (C,H3)C2,0,.3H0. And by further substitution of an atom of peroxide of hydrogen for an atom of hydrogen in the acetyl oxyacetic acid is formed a corn-pomd which indeed Wurtz actually obtained as a product of the oxidation of hydrated oxide of ethylene.To these observations it may be objected that Debus’s glyoxd C,H,O, is the aldehyde which atands between hydrated oxide of ethylene and oxyacetic (glycollic) or oxalic acid (whichever of these c2 KOLBE ON THE acids may now he regarded as corresponding to hydrated oxide of ethylene or to glyosal). But before entering upon this question it mould be well to decide whether we are justified in regarding glyoxal as an aldehyde. The property of passing by oxidation into one or two acids richer in oxygen than itself and that of uniting with alkaline bisulphites are possessed by glyoxal in com-mon with many other bodies which are not aldehydes. But even granting that glyoxal may be an aldehyde it is certainly not the aldehyde of hydrated oxide of ethylene or of oxyacetic glyoxylir or oxalic acid.Whatever view we may take of its constitution the process by which it is converted into oxyacetic acid is certainly quite unlike the formation of acetic acid from aldehyde for the latter is simply a process of oxidation consisting in the mere assumption of 2 atoms of oxygen ;whereas the former depends upon the addition of 2 atoins of water to the constituents of glyoxal C,€I,O,& + 2H0 = H0,C4H,0 GIyoxal. Oxyacetic acid. I regard glyoxal provisionally as constituted according to the formula (C2 {EO,)C,O, that is to say as the bioxide of the biiltomic radicle (C2 f €1 )C2 in which the member WO (.C2 osymethylenc,-a derivative of methylene C2H2,-is combined with carbonyl.The transformation of glyoxal into oxyacetic acid may then be rationally expressed by the following equatioii :-Glyoral. Oxyncetic acid. With respect to the chemical constitution of the so-called glyoxy- lic acid I suggest that it may be a further substitution-product of acetic acid of the same kind as oxyacetic acid viz. bioxyacetic acid HO. (C HO C,O,,O = H0.C4H30, that is to say go) acetic acid having 2 At hydrogcn in the radicle replaced by 2 At. peroxide of hydrogen :- CONSTITUTION OF LACTIC ACID. HO. (C2II,)C,O2,O Acetic acid. (:a,) 110.(C C,O,,O Oxyacetic (glycolic) acid. C,O,,O Bioxyacetic (glyoxylic) acid. HO Similarly I am of opinion (and am at present engaged nith experiments relating to the matter) that ylyceric acid discovcrcd not long ago by Debus is bioxypropionic acid and that it stands to lactic and propionic acid in tlie same relation as bioxyacetic acid to oxyacetic and acetic acid HO.(C,H,)C,O,,O Propionic acid. HO.(C {E~,)c,o,,o oxypropionic (lactic) acid. HO.( C HO C,O,O Bioxypropionic (glyceric) acid. g;) If t-lowever-and of this I am convinced-oxyacetic and oxypro-pionic acid do uot stand to hydrated oxide of ethylene and hydrated oxide of propylene in the same relation as acetic and propionic acid to ethyl-alcohol and propyl-alcohol it still remains a question whether the aldehydes and alcohols correspondiiig to osyacetic and oxypropionic acid have any existence. Of this I have no doubt and even consider it easy to prcdict how these aldehydes and alcohols must be constituted.With regard to their empyrical constitution they mill bear to oxyacetic and oxypropionic acid the sanie relation that the cmpyrical forinulte of aldehyde and ;tlcohol bear to that of acetic acid that is to say they will differ from the corresponding compounds of the acetic acid series by containing 2 additional atonis of oxygen as may be seen from the filloaing table :-HO.C,H,O C4H40 C4H50.H0 Acetic acid. Acetic aldehyde. Acetic (ethjlic) alcohol. HO.C,H,O C*H*O* C4H503. HO Oxyacetic acid. Oxyacetic aldehyde. Oxyacetic alcohol ICOLBE ON THE H0.C6H503 C6H602 C,H,O.HO Propionic acid. Propionic aldehyde. Propionic alcohol. HO.C,I-I,O W60 C6H,0,.H0 Oxypropionic acid.Oxypropionic aldehyde + Oxypropionic alcohol. Among known compounds anisic acid nnisic aldehyde and anisic alcohol may be mentioned as similarly related :-H0.c 6H,O C,,H,O C~~H~O~.KO Anisic acid. Anisic aldehyde. Anisic alcohol. It may also be observed that anisic acid is related to toluylic acid so far as its rational constitution is coricerned-in the same manner as oxypropionic acid to propionic acid-and that generally the aldehydes and alcohols of osyacetic oxypropionic acid and anisic acid may he regarded as derivativesof the primary aldehydes and alcohols in the same sense as the oxyacids themselves are derivatives of acetic propionic and toluylic acid. The following formulae are given as the symbolic expression of my views of the rational constitution of thew compounds :-Acetic acid.Acetic aldehyde. Acetic (ethylic) alcohol. (c {5,}C2O2 Oxyacetic acid. Oxyacetic aldehyde. Oxyacetic alcohol. Propionic acid. Propionic aldehydc. Propionic alcohol. Oxypropionic mid. Oxypropionic aldehydc. Oxypropionic alcohol. Toluylic acid. Toluylic alcohol. Toliiylic alcohol. * Oxypropionic aldehyde wouId be isomeric with hydrated propionic acid acetate of methyl and formatc of ethyl ;oxyacetic aldehyde with hydrated acetic acid $c. CONSTITUTION OF LACTIC ACID. Anisic acid. Anisic aldehyde. Anisic alcohol. The fundamental idea of these formulze of alcohols and altle-hydes will be more fully developed in a future communication.