386 DAWSON AND MARSHALL: THE REACTIONX LIL-- The Reaction Bettoem Iodine and AliphaticAldehydes.By HARRY MEDFORTH DAWSON and JOSEPH MARSHALL.THE only account of experiments on the action of iodine in ali-phatic aldehydes was published in 1889 by P. Chautard (An?L.Chim. Phys., 1889, [vi], 16, 656), and a r6sum6 of Chautard’sresults is necessary to explain our re-investigation of this reaction.This observer obtained monoiodo-substituted aldehydes by allowingiodine and iodic acid to remain in contact with a dilute alcoholicsolution of an aldehyde for some time a t the ordinary temperature,and he was unable to obtain further substitution by increasing theproportion of iodine and iodic acid reacting with the aldehyde.The monoiodo-aldehydes were unstable substances, which could notbe distilled without decomposition, and of those which he described,the iodopropionaldehyde was the most stable.With regard t otheir constitutioiz, Chautard makes certain statements which seemto us to be of considerable interest. There can be 110 question ofthe constitution of a mono-substituted acetaldehyde, but the caseis, of course, different with the higher aldehydes. Chautard statesthat on boiling iodopropaldehyde with dilute nitric acid, it isconverted into @-iodopropionic acid, melting at 8Z0, and he con-cludes that the aldehyde is, therefore, the P-compound,CH,I*CH,*CHO.I n the case of iodoisobutyraldehyde, Chautard was unable to isolateany @-iodobutyric acid from the products of oxidation, but lieassumed that the iodobutyralhhyde is also a @-compound, namely,CH,-CH(CH,Ih *CHO.Further, Chautard obtained an iodovaler-aldehyde which, from analogy t o a chlorine derivative described byPopoff and Pavleski (Ber., 1576, 9, 1606), he assumes is theBETWEEN IODINE AND ALIPHATIC ALDEHYDES. 387a-derivative, CH(CH,),*CHI*CHO, and in the case of heptalde-hyde he assigns to the iodine derivative the formula(‘sous toutes r8serves.”Apart from the fact that Chautard assigns formulze to twoiodoaldehydes which show them to be a-derivatives, whilst intwo more cases he assigns formulae showing them to be 8-deriv-atives, it seemed of interest to us to re-investigate the question,since the production of 8-substituted derivatives would bedifficult to reconcile with a theory of substitution analogousto that adopted by one of the authors in the case of the actionof a halogen on an aliphatic ketone (T., 1909, 95, 1860). I nthis reaction, it is assumed that the ketone changes into itstautomeric enolic form, and that then a molecule of halogen isadded on a t the double linking.Finally, the elimination of amolecule of halogen acid results in the formation of the substitu-tion product, which must necessarily have the halogen atomattached to the a-carbon atom. A scheme showing this series ofreactions would be:CH,*[CH,],*CHI*CHOR-CO*CH, + R*C(OH):CH, -+ R*C(OH)X*CH,X +R*CO*CH,X(where X = halogen).Since Chautard described iodopropaldeliyde as the most stable ofthe iodo-aldehydes which he prepared, and was the only one inwhich he carried out experiments to determine the constitution ofthe substance, it was decided to investigate this aldshyde.Thirty grams of propaldehyde were mixed with 85 C.C.of 90 percent. alcohol, after which 41.5 grams of iodine were added, andfinally 16.5 grams of iodic acid. The mixture was allowed toremain, with frequent shaking, a t a temperature of from 1 8 O to20° for about fourteen days. After this period the solid iodineand iodic acid had disappeared, and the mixture was of a darkbrown colour. Water was added, and the heavy oil which was thusprecipitated was separated, washed with very dilute sodium car-bonate solution, and finally dehydrated over sodium sulphate.The iodo-aldehyde, contrary to Chautard’s statement, can bedistilled under diminished pressure, and was obtained as an almostcolourless liquid, boiling a t 83--84O/17 mm.I n one experimentthe yield was more than 30 grams, but in most cases only about15 grams of iodo-aldehyde were obtained from 30 grams of prop-aldehyde. The iodo-aldehyde was boiled with dilute nitric acid(1HNO3:4H,O) under reflux until iodine began to separabe, anda clear solution had been obtained. On cooling, the liquid wasfiltered and extracted with ether. The ethereal extract was washe388 REACTION BETWEEN IODINE AND ALIPHATIC ALDEHYDES.with dilute sodium carbonate solution in order to remove the acidfrom any unchanged aldehyde. After acidifying the alkalinesolution, it was extracted with ether, and subsequently, afterdehydration of the solution, the ether was removed by heating ina vacuum on a water-bath.The residual oil was allowed to remainfor several days in the ice-chest, but no crystallisation occurred,although a trace of /3-iodopropionic acid was added t o induce crys-tallisation. This oil was completely soluble in dilute ammonia ordilute sodium carbonate solution, but it was not very soluble inwater. After boiling the acid with dilute sodium carbonate solu-tion, cooling, and acidifying with dilute nitric acid, the additionof silver nitrate solution caused the precipitation of silver iodide.This reaction was used as a means of identifying the acid, whichwas boiled with sodium carbonate solution, acidified, and extractedwith ether.The liquid remaining after the removal of the etherwas identified as lactdc acid. It gave carbon monoxide when itwas heated with concentrated sulphuric acid, whilst boiling withthe dilute acid 1iberat.ed acetaldehyde and formic acid. The zincsalt was obtained and compared with zinc lactate, and was foundt o be identical.There can be no doubt, then, that the product of the action ofiodine on propionaldehyde is a-iodopropaldehyde.9 reaction which is described in Chautard’s memoir (Zoc. c i t . ) isthat of silver acetate on the iodo-aldehydes. Instead of obtainingthe acetyl derivatives of the hydroxy-aldehydes as would beexpected, Chautard claims t o have obtained the acetate of thealcohol corresponding with the aldehyde with which he was experi-menting; for instance, by allowing silver acetate to react withiodoacetaldehyde, he obtained ethyl acetate, whilst in a similarmanner from iodopropaldehyde, isopropyl acetate was produced.Chautard makes no attempt to explain the mechanism of thisreaction, and without attempting to do so, we think that theassumption is justified that the acetyl group would attach itselfto that carbon atom of the aldehyde t o which the iodine atom waspreviously linked.I n that case, accepting Chautard’s statementthat his iodopropaldehyde was the 8-derivative, he should haveobtained n-propyl acetate by the action of silver acetate, whereashe actually obtained isopropyl acetate.For thispurpose, iodoacetaldehyde was made according to Chautard’smethod.The reaction product was poured into water, andextracted with ether (free from alcohol). The ethereal solution wasdecolorised by washing with sodium thiosulphate solution, and,after dehydration, it was boiled under reflux on the water-bathIt seemed desirable, therefore, to repeat this reactionWATSON AND SEN: DYES DERIVED FROM QUERCETIN. 389with exces of silver acetate, until no appreciable amount of iodinewas left in the ethereal solution. The silver iodide was filtered off,the ether distilled off on a water-bath, and heating on the water-bath was continued until nothing further distilled. The tempera,ture of the yapour did not rise above 53*, so that no ethyl acetatecould have been present, a result which had been expected fromthe absence of the slightest odour of this substance. The residueleft after the evaporation of the ether was a yellow, viscous liquid,which distilled in a vacuum when heated on a water-bath, and i tdistilled a t the atmospheric pressure between 1 0 8 O and 1 1 2 O .The distillate was a colourless liquid with a pungent odour, butthis may have been due to the presence of a trace of unchangediodoacetaldehyde, as a little iodine was found in it. This liquidgave all the reactions of an aldehyde, and when heated with absolutealcohol and a little concentrated sulphuric acid, the odour of ethylacetate was observed.The phenylhydrazone was obtained as a faintly yellow substance,readily soluble in alcohol or ether, but not very soluble in lightpetroleum, and it melted a t 128O. Although no analysis was madeof the substance, there is every reason to assume, that the reactionbetween the iodo-aldehyde and silver acetate proceeds quitenormally, instead of abnormally, as stated by Chautard.THE UNIVERSITT, LEEDS