Report of Synthetical Researches on Organic Acids. By ALFRED R. CATTON, M.A., F.R.S.E., Fellow of St. John's College, Cambridge. 1. Ar the Dundee Meeting of the British Association in September 1867, I was requested to continue my researches on the action of carbonic acid and sodium on alcohol, and a grant was placed at my disposal for the purpose. This Report is presented to the Association in compliance with the law which requires that, when a grant of money has been made at one Meeting, a Report of the progress of the research shall be presented at the next Meeting. 2. One principal object of my labours during the past year has been to convert as large a proportion as possible of the sodium used in the reaction into organic salts, and I am now able to report that, instead of obtaining from 100 grammes of sodium only 7 grammes of sodium-salts of acids formed synthetically, I have succeeded in obtaining 175 grammes. To give an account of the conditions necessary to this result, and of the experiments by which it is established, is the object of this Report. 3. My previous experiments had shown that, in order to obtain the largest quantity of synthetically formed salts, it was necessary, (1) That the action of the sodium on the alcohol be modified as much as possible, and with this object the sodium was added gradually and in small pieces. (2) That the temperature of the alcohol be kept as low as possible, by surrounding the Woulfe's bottle containing it with a mixture of ice and salt. The manner in which this last condition influenced the reaction was no doubt by increasing the amount of carbonic acid which the alcohol dissolved. It tended also to modify the action of the sodium. Now it occurred to me that the most effectual way to modify the action of the sodium, was to use sodium-amalgam containing such a small percentage of sodium that it might act almost imperceptibly on absolute alcohol. I therefore determined to use sodium-amalgam containing about 2 per cent. of sodium. 4. The apparatus used was very simple. Carbonic acid, from a gasogene, was washed and dried. The gas was then passed through a refrigerator, which consisted of a large wooden box lined inside with zinc, and containing a long spiral leaden tube. Ice was put into the box, and surrounded the tube, and thus the gas, on emerging from the refrigerator, was at 0° C. The refrigerator served also as a storehouse for the ice, and in it 50 lbs. of ice could be kept for several days without being all melted. The gas was then passed through a series of Woulfe's bottles, surrounded with ice and salt, contained in a wooden trough lined with zinc, and covered with a wooden lid. 5. Absolute alcohol was obtained from Messrs. T. & H. Smith, of Edinburgh, of sp. gr. 7957 at 60° F. It was distilled from sodium, and its sp. gr. was then 7940 at 60° F. Sodium-amalgam was prepared by heating mercury, and then adding sufficient sodium to make an amalgam of about 2 per cent. The amalgam was subsequently fused to render it of uniform composition, the fluid part poured on a slab, and, when cool, placed in bottles containing dry carbonic acid. The amalgam was uniformly crystallized in slender needles, which had not tarnished in the slightest degree when used. 6. In order to determine the amount of sodium used in the reaction, it is necessary to know accurately the percentage of the sodium in the amalgam. Two determinations of this percentage were therefore made. I. 10-4695 grms. of the amalgam were left in contact with standard sulphuric acid, and, when gas ceased to be evolved, excess of acid was titrated with standard caustic soda. It was thus found that 10-4695 grms. contained 1794 grm. sodium. The amalgam therefore contained 1.714 per cent. sodium. II. 8·015 grm. amalgam were boiled in a flask with water till there was no perceptible evolution of gas. The caustic soda produced was titrated with standard sulphuric acid. It was thus found that 8-015 grms. contained 1403 grm. sodium. The amalgam therefore contained 1.750 per cent. sodium. The mean of these determinations gives 1.732 as the percentage of sodium in the amalgam. 7. One hundred cub. centims. absolute alcohol were added to each of eight carefully dried Woulfe's bottles. Carbonic acid was passed for an hour, in order thoroughly to saturate the alcohol, and then sodium-amalgam added to each bottle by means of a glass-stoppered neck. For reasons which will be subsequently understood, the last four bottles were detached after about twelve hours, and the reaction went on in them without any more carbonic acid being passed. The gas was passed through the other four bottles for three days, the temperature of the alcohol, for nearly the whole time, being several degrees below 0° C. 8. Before describing the method of examining the product of the reaction, a few words of explanation are necessary. If sodium is dissolved in absolute alcohol, sodium-alcohol is formed and hydrogen given off. If dry carbonic acid be passed into the sodium-alcohol, the sole product is ethylcarbonate of sodium, to which has been assigned the formula CO, No. Na 0. This compound is decomposed by acids into alcohol and the sodium-salt of the acid; by oxalic acid, for instance, into alcohol and oxalate of sodium. 2 Now if a known weight of sodium be added to absolute alcohol, and whilst the sodium is dissolving a current of dry carbonic acid be passed, it is found that the number of cub. centims. of standard acid required to neutralize the ethylcarbonate is less than is equivalent to the sodium used. If W be the weight of sodium used, and the number of cub. centims. of standard oxalic acid, containing 63 grms. crystallized oxalic acid in the litre, required to neutralize the ethylcarbonate, x×023 is less than W, and W-x×·023 is the amount of sodium incapable of neutralizing standard acid, and which, in fact, exists as sodium in salts of acids formed synthetically. 9. If sodium amalgam and carbonic acid act upon alcohol, in order to determine the sodium used in the reaction, we must know,— i. The amount of sodium in the sodium-amalgam. This is determined by calculation from the weight of amalgam used and the percentage of sodium it contains. ii. The amount of sodium left in the amalgam after stopping the reaction. This is determined by leaving the residue of amalgam in contact with standard sulphuric acid, and determining excess of acid by standard caustic soda. i. minus ii. gives (w) the sodium used in the reaction; and if, as before, a be the number of cub. centims. standard oxalic acid required to neutralize the ethylcarbonate, w-xx023 is the sodium converted into salts of organic acids. It is assumed in the above that an amalgam can be made of uniform composition, or nearly so, as, in fact, my experiments have shown. Experience shows that the operations, as above described, can be carried out so as to give results of great nicety. Oxalic acid is used in these determinations on account of the sparing solubility of oxalate of sodium in water and alcohol, which enables us to separate it at once from the sodium-salts formed synthetically. 10. We now proceed to state the results of the examination of the contents of the several bottles. The products of the reaction in the first four bottles were added together, the amalgam in each bottle being rapidly washed with water, so that as little as possible of the sodium it contained might appear as caustic soda in the washings. 430.5 cub. centims. oxalic acid were required to render the solution neutral, as determined by very delicate neutral test-paper. Therefore Na as ethylcarbonate=9.90 grammes. 740 cub. centims. standard sulphuric acid were required to neutralize sodium which remained in amalgam, which was therefore 17.02 grms. 11. The amount of sodium originally contained in the amalgam was determined from the weight of mercury left after extracting the sodium from the amalgam. If (Hg+Na) denote the weight of sodium-amalgam used, and (Na) the sodium contained therein, we have (Hg), the weight of mercury, was found to be 1954-84 grms.; Hence 34-45 grms. sodium were contained in amalgam used. From this, subtracting 17-02, the sodium left in amalgam, we get 17.43 grms. as the amount of sodium used in the reaction. Of these 17.43 grms. sodium 9.90 were converted into ethylcarbonate. Therefore the remaining 7.53 grms. existed as sodium in salts of acids formed synthetically. = Hence 56.22 percentage of sodium converted into ethylcarbonate, and salts of organic acids. 43.78= وو 12. We now proceed to find the total weight of salts formed synthetically. For this purpose advantage is taken of the sparing solubility of oxalate of sodium in alcohol. Three solubility determinations at the ordinary temperature gave the following results :— 1 part oxal. of Na dissolves in 143 pts. by weight of alcohol of 20 per cent. The solution containing the products of the reaction, after neutralization with oxalic acid, was evaporated to dryness, and the residue treated with alcohol of 20 per cent., which dissolves the salts formed synthetically, and leaves pure oxalate of sodium, as the following analysis shows:: 522 grm. of the residue gave 5475 grm. Na, SO, or ∙1774 Na. The salt therefore contained 34-11 per cent. Na. Oxalate of Na contains 34-33 per cent. Na. The solution in alcohol of 20 per cent. was evaporated to dryness, and heated till it ceased to lose weight in a weighed crucible, a little absolute alcohol being added to facilitate the drying of the deliquescent residue. Weight of organic salts=22-32 grms. Now 23 grms. sodium correspond to 112 sodium ethylcarbonate. Hence the weight of ethylcarbonate corresponding to 9.90 grms. sodium is 48-21 grms. Hence as from 17.43 grms. sodium are obtained 22-32 grms. organic salts, and 48.21 grms. sodium ethylcarbonate, from 100 grms. sodium would be obtained 128.06 grms. organic salts, and 276.59 grms. sodium ethylcarbonate. 13. If, now, the organic salts be decomposed by a solution of oxalic acid in alcohol of 60 per cent., containing just sufficient oxalic acid to convert 7.53 grms. sodium into acid oxalate, the sodium is converted into acid oxalate, and the acids remain in solution. On distilling the acid solution, alcohol goes over accompanied by the volatile acids. If water be added to the retort till the liquid which distils over is very faintly acid, the distillate contains the whole of the volatile acids, and the fixed acids remain in the retort. The acid distillate required for neutralization 148 cub. centims. standard caustic soda, which are equivalent to 3.40 grms. Na; therefore, 3.40 grm. Na existed in salts of volatile acids. Now 7.53 was the whole quantity of sodium in organic salts. Hence, of the sodium in organic salts, 45.15 per cent. existed in salts of volatile acids, and fixed acids. 14. The solution of sodium-salts of volatile acids was evaporated to dryness, and dried till it ceased to lose weight. Weight of residue=10.37 grms. ; and as the total weight of organic salts was 22:32 grms., 11.95 grms. were salts of fixed acids. Hence, of the total organic salts, 46.46 per cent. were sodium-salts of volatile acids, and fixed acids. 15. The results of the examination of the remaining bottles will not be given in detail. They are collected in the following Table, the first vertical column containing the results of the examination of the first four bottles, and the other columns those of the last four bottles:— 16. Now carbonic acid was passed through the last four bottles for several hours and then stopped, the sodium-amalgam continuing to act on the contents of each bottle for about two months till it contained no more sodium. From the last four columns of the Table we see that thus a much larger proportion of sodium is converted into ethylcarbonate and a much smaller proportion into organic salts. Whence we conclude that the proportion of sodium converted into organic salts is much increased by keeping a current of carbonic acid constantly passing through the alcohol. 17. It will be observed that the proportion of the fixed to the volatile acids diminishes from the second to the last column. This result is difficult to explain; but other observations tend to throw light on the conditions which determine the proportion of the fixed to the volatile acids in the ultimate product. 18. The results of the foregoing experiments indicated the possibility of converting a still larger proportion of sodium into organic salts. I therefore determined to repeat the reaction, taking advantage of the experience gained both during the reaction and the subsequent analytical operations. 19. Two determinations were made of the percentage of sodium in the amalgam used in the reaction to be now described, and to render them as accurate as possible much larger quantities of amalgam were analyzed. They were made as before, by leaving the amalgam in contact with standard sulphuric acid and determining excess of acid by standard caustic soda. I. 286-97 grms. amalgam required for neutralization 202.9 cub. centims. standard acid, which are equivalent to 4.668 grms. Na. Therefore 100 grms. contained 1.626 grm. Na. II. 135.05 grms. amalgam required for neutralization 96.1 cub. centims. standard acid, which are equivalent to 2.21 grms. Na. Therefore 100 grms. contained 1·636 grm. Na. The mean of these two closely concordant determinations gives 1·631 as the percentage of sodium in the amalgam. 20. 1420-8 grms. of this amalgam were put into a large Woulfe's bottle, and 500 cub. centims. absolute alcohol added. Carbonic acid was kept constantly passing through the alcohol for three days, the apparatus being the same as before. 21. To the product of the reaction in the Woulfe's bottle 250 cub. centims. standard oxalic acid were added, and a rapid current of air blown through the liquid, which was then found to be acid, and required for neutralization 2 cub. centims. standard caustic soda. Hence 248 cub. centims. standard acid were equivalent to sodium as ethylcarbonate, which was therefore 5.70 grms. The contents of the bottle were then transferred to a beaker and the amalgam washed with water. Some of the sodium left in the amalgam thus |