HOWARD ON THE HISTORY OF CINNAMIC ACID. 135 XVI.-Contribution towards the history of Cinnamic Acid. BY DAVIDHOWARD. NOTWITHSTANDING the experiments of Gerhardt and Cahours and the subsequent researches of Blyth and Hofmann the history of cinnamol and its derivatives is far from being complete. To fill up some of the gaps still existing I engaged in some experi- ments upon this interesting group of substances. In the prosecu-tion of my enquiry I had an opportunity of observing some facts which I beg to lay before the Chemical Society. Liquid storax treated in the usual way afforded the crude * A drop placed beneath the tongue destroys the epidermia and causes a soreness which lasts many days. ROWARD ON THE cinnamic acid for the experiments.For the purpose of purify-ing it I adopted the plan recommended by some chemists of submitting the crude product to careful distillation. To my surprise a large portion of the distillate came over in the form of a permanent liquid. The smaller portion which so!idifieci on cooling was purified by crystallisation and converted into a silver salt. The silver determination gam the following result *2090grm. of the silver-salt left on ignition *Q9850grm. = 47.13 per cent of metallic silver. The percentage of silver in benzoate of silver being 47.16 it was obvious that the solid distillate consisted of benzoic instead of cinnaniic acid. To find whether this benzoic acid was present in the original crude acid or whether it had been formed by the destruction of cinnamic acid a portion of the crude acid was recrystallized and converted into a silver-salt.05735 grm. of this salt left on ignition *2500grm. of metallic silver = 43.59 per cent. 42-37being the percentage of silver in cinnamate of silver it could not be doubted that the crude acid employed contained an appreciable admixture of benzoic acid. It was therefore further purified by solution in alcohol and crystallisation by epontaneoris evaporation of the solvent when large regular crystals were obtained which on analysis of a new silver-salt proved to be purc cinnamic acid. *ti170grm left .It190 = 42.36 per cent. of silver *SO85grm. left ,2150 = 42.28per cent. of silver. These numbers coincide with the theoretical percentage of cinnamate of silver.A careful distillati611 of this pnye acid afforded together with a large portion of an oily product a small quantity of an acid mliich solidified in the neck of the retort. This acid was converted into a silver-salt and in this form submitted to analysis :--2255 grm. left on ignition -0955 = 42-35 per cent. of silver -2165 grm. left on ignition 9915 = 42-27per cent. of silver. The distilled acid was therefore undecomposed cinnamic acid. In other experiments in which the acid was submitted to a still slower distillation the whole of it was entirely decomposed and converted into liquid products of decomposition. RISTORY OF CINNAMIC ACID. 13'7 Thus it would appear that cinnamic acid contrary to the state- ments of most Manuals is decomposed when kept at a boiling heat and that it can only be distilled even partially unchanged when very rapidly heated care being taken to carry over the vapour as quickly as possible by keeping the upper part of the retort at a very high temperature.In order to find whether cinnamic acid would decompose when maintained for a long period at a somewhat lower temperature a portion of the acid was sealed up in a glass ttibe and heated for several hours to 200"C. in a paraffin bath ; no change however took place. Another portion was similarly heated in presence of water. It remained likewise unchanged the silver-salt yielding the following percent age :-*4805grm. gave -2040 =I 42.45per cent of silver. The fluid which is formed by the action of' heat upon cinnamic acid proved on investigation to be almost pure cinnamol; the boiling point remained constant at 145" C.till the greater part of the liquid had passed over when the temperature rose rapidly leaving in the retort a resinoid mass of metacinnamo2. By treat- ing the liquid with bromine the characteristic crystalline dibromide of cinnamol was obtained; and by exposing a portion sealed up in a tube to 200° it was entirely converted into a glassy mass of metacinnamol which when submitted to a still higher temperature was reconverted into cinnamol. These properties identify the oily product of decomposition of cinnamic acid with cinnamol or what is the same thing with styrol although it appears that the tendency to pass into the solid condition is perhaps leas marked in this liquid than in styrol a fact noticed by other observers in cinnamol foymed by the usual process.When very carefully heated cinnamol obtained by the destructive distillation of cinnam'lic acid may be almost entirely distilled without the production of the solid modification. The preceding experiments prove that at a temperature very near its boiling point cinnamic acid is decomposed into cinnamol and carbonic acid according to the equation a decomposition similar to the transformation into benxol and carbonic acid which benzoic acid undergoes when its vapour is passed through a red hot tube. HOWARD ON THX The cinnamol thus obtained from cinnamic acid amounts to from a fourth to a third of the acid employed so that this reaction furnishes a method of preparing cinnamol much more easily and much more copiously than it could be hitherto obtained.Cinnarnol obtained in this manner is perfectly free from benzol. It is well known that the liquid obtained by the usual process viz. distillation of cinnamic acid with lime and even baryta consists of a mixture of hydrocarbons in which so large a proportion of benzol is present that some chemical Manuals state the boiling point of cinnamol at 89" C. proving that the proportion of cinnamol in these mixtures is excessively small. The dry distillation of pure cinnamate of lime likewise furnishes cinnamol qiiite free from benzol thus affording a remarkable contrast to the behaviour of a mixture of cinnamic acid and excess of lime.The crude cinnamol obtained from either cinnamic acid or cinnamate of lime contains a small quantity of a crystalline substance which may be separated from the more volatile cinnamol by distillation with water ;the formation of metacinnamol is thus in a great measure prevented arid the substance in qiiestion may be extracted from what is left in the retort by alcohol from which it crystallises. When purified by several crystallisations from boiling alcohol which dissolves it freely while cold alcohol retains a comparatively small portion the crystallirie substance presents itself in the form of brilliant pearly scales which on analysis gave the following results :-I. '1563 grm. gave *5341carbonic acid and *0992water.11. -2500 grm. gave -8605 carbonic acid and ,1545water. These numbers represent a hydrocarbon C,,H6 or a multiple of it Theory Experiment c,* I. 11. 84 93.33 93-19 93.76 6. 6.67 7*05 6.86 H6 -. -90 100~00 The crystalline substance when gently heated with bromine gives rise to the formation of a bromine-compound which is only slightly soluble even in boiling alcohol. The hot solution deposits on cooling minute scales exhibiting a slightly reddish tint. On analysis the following results were obtained :- HISTORY OF CINNAMIC ACID I. -2780grm. gave *5060carbonic acid 0.985water 11. *1915grm gave 02120bromide of silver 111. *2020grm. gave 02255bromide of silver. The formula C,,H6Br requires the following values which 1 place in juxtaposition with the experimental numbers :-Theory Experiment 7 I 11.111. 84 49.41 4964 .-c1* . 6 3.53 3.68 -H6 Br . . 80 47.06 -47.10 47.50 -7-170 100.00 The formation and composition of the bromine-compounds could leave but little doubt that the crystalline hydrocarbon must be represented by the formula C2*H12. A hydrocarbon of precisely the same composition and exhibiting also the general characters of the substance derived from cinnamic acid was described some years ago by Laurent. He obtained the body which he calls cCstilbene,” together with another crystalline body ‘‘thionessal,” in the destructive distillation of hydride of sulphobenzoil thus Eydride of Sulphobenzoll Stilbene Thionesml 8C14H6S2= 2c,s4 4-6HS 4-2C,,HI2 3-C,2H,,S2* In order to establish the identity of the two substances I have prepared a quantity of stilbene according to Laurent’s process In repeating the experiments of Laurent I observed all the phenomena described by that chemist.On comparing the stilbene procured in this manner with the crystalline substance obtained from cinnamic acid it was impos-sible to doubt their absolute identity. I have nothing to add to Laurent’s description except that stilbene prepared by the dry distillation of either hydride of sulphobenzdil or of cinnarnic acid fuses at 125”C. The transformation of cinnamic acid into stilbene is obviously the result of a destructive process which does not admit of simple representation in formulae. The experiments which I have described were performed in Dr. Hofm a n n ’s laboratory.