in the production of ether, would follow from the relatively small tendency of the alcohol to form intermediate silver salts.

The formation of unstable silver salts of esters of hydroxy-acids may afford an explanation of the production of esters of alkyloxyacids in the interaction of silver salts and alkyl iodides (Purdie and Lander, Trans., 1898, 73, 289). We may imagine in this instance that the ester of the hydroxy-acid, in virtue of its feebly acidic. character, enters into double decomposition according to the reversible reaction:

The silver compound of the ester would then undergo further reaction with the alkyl iodide, yielding the alkyloxy-ester. The production of alkyloxy-esters in the interaction of iodides and oxysilver salts is accompanied in all cases by the production of free organic acid, and the amount of alkyloxy-ester produced varies with the amount of free acid obtained. This fact finds ready explanation by the assumption here made. The explanation, it is true, scarcely covers the fact that free alkyloxy-acid is also found, although in very much smaller proportion, along with free hydroxy-acid.

Free alkyloxy-acid might, however, result from the partition of the ethyl group between the free hydroxy-acid and alkyloxy-ester:

or more simply by the partial hydrolysis possibly effected by the dry potassium carbonate, used in the removal of free acid from the product.

It must be pointed out that the greater production of free acid in the action of isopropyl than in that of ethyl iodide, may be due to the decomposition of the iodide CH, CHI CH2 =HI+CH, CH:CH2. The corresponding reaction with ethyl iodide is not, however, so likely to occur.

3

If this view of the reactions in question be correct, it might be expected that the formation of esters of alkyloxy-acids could be brought about by the joint action of ethyl iodide and the silver salt of a weak acid on an ester of a hydroxy-acid. As a test case, the action of silver carbonate and ethyl iodide on ethyl tartrate was examined. No action occurred in the cold during one hour with a mixture of 39 grams of silver carbonate, 20 grams of ethyl tartrate, and 44 grams of ethyl iodide. On boiling, a moderately energetic

VOL. LXXVII.

3 F

action set in, the yellow silver salt rapidly darkening, and eventually turning black. The product, after 4 hours boiling, was a viscid, neutral liquid. After removal of ethyl carbonate in a vacuum, the bulk of the substance distilled over between 151° and 154° under 11 mm. pressure. In a 100 mm. tube at 20°, the liquid gave a +32·02°. Ethyl tartrate gives at the same temperature ap +9.13°, and ethyl diethoxysuccinate at 18°, a +97·52° (Purdie and Pitkeathly, loc. cit., 159). The notable increase in rotation caused by the action of silver carbonate and ethyl iodide is attributable most simply to the formation of roughly 25 per cent. of dialkyloxy-ester.

A mixture of silver acetate, ethyl tartrate, and excess of ethyl iodide was similarly boiled for 3 hours. Free acid resulted as one of the products, and was removed by potassium carbonate. About onehalf of the neutral product consisted of unchanged ethyl tartrate (a+9.25°); the remainder was a thick, tarry mass, which could not be distilled in a vacuum. Apart from the small likelihood of partition of silver occurring between a strong acid, such as acetic, and a hydroxyester, the fact that the reaction apparently pursued a different course from that anticipated renders the result of the experiment inconclusive.

The results obtained with ethyl acetoacetate are of interest with respect to the question of the probable constitution of this substance. Physical considerations are regarded as proving that ethyl acetoacetate consists mainly of the ketonic form, mixed, however, with a small proportion of the enolic form, the substance presenting an instance of equilibrium of the unimolecular type, as suggested by Traube (Ber., 1896, 29, 1715). The failure of chemical methods of proof of the presence of the two dynamic isomerides in ethyl acetoacetate is attributable in great measure to the fact that a substituting agent usually acts exclusively with one or the other form, as is well shown in the case of diazomethane (von Pechmann, loc. cit.). In this particular instance, the equilibrium law would lead us to expect that, as soon as the enolic form has been rendered stable by conversion into methoxycrotonate, more of the enolic form will be produced from the ketonic form, in quantity depending upon the coefficients of velocity of the two isomeric changes, until eventually the whole of the substance has reacted in the enolic form. Such considerations (compare Lowry, Trans., 1899, 75, 241) serve to account for the influence of the so-called ketonising and enolising agents in determining in which form condensation with benzalaniline shall ensue (Schiff, Ber., 1898, 31, 207, 601). Similarly, in the interaction of ethyl acetoacetate with ethyl orthoformate, even although some proportion of the substance were initially present in the hydroxy-form, in so far as the orthoformate appears capable of reaction only with the ketonic form

(Claisen, Ber., 1896, 29, 1005), eventually the whole of the acetoacetate will have reacted in the latter form. Granting that alkylation by means of silver oxide and iodides depends upon the preliminary formation of silver substitution compounds of types corresponding to those of the alkyl derivatives eventually obtained, the simultaneous production from ethyl acetoacetate of both O'C2H, and C.C2H, homologues, points to the prior formation of the two silver salts, CH, C(OAg):CH.CO2C2H, and CH,•CO CHAg•CO,C,H, and therefore to the existence of both ketonic and enolic forms in the original substance. If the silver oxide is assumed to act merely by elimination of the elements of hydrogen iodide, the conclusion is more direct, or even unavoidable. The elements of hydrogen iodide would be removed from the ethyl iodide and the replaceable hydrogen atom of the two characteristic groupings •CO·CH2 and C(OH):CH, and the results obtained would therefore indicate the presence of both these groups in ethyl acetoacetate. As stated above, the view that silver derivatives are actually formed is adopted here.

In cases of syntheses effected by the aid of metallo-derivatives, such as the formation of alkyl homologues from ethyl sodioacetoacetate, in so far as only one type of alkyl homologue is produced, it is possible to explain its formation either by the ONa or CNa constitution for the sodium salt. Where both types of derivative are produced, as, for example, in the action of ethyl chlorocarbonate on ethyl sodioacetoacetate (Claisen, Ber., 1892, 25, 1768), and in the action of acetyl chloride on the sodium and copper compounds (Nef, Annalen, 1893, 276, 222), it may be assumed (Nef) that the interaction is of two distinct kinds, namely, double decomposition, and replacement with prior addition. The assumption, certainly by no means improbable, is here made that two definite substances interact, not in one, but in two senses, the course of the reaction of silver oxide and ethyl iodide with ethyl acetoacetate being admittedly susceptible of explanation in the two following ways:

Similar equations would serve to account for the formation of both types of ethyl compound, using the CH, CO-CHAg CO2CH, formula,__ if the elements of C2H,I in the indirect action are assumed to be

added on to the CO group. In conformity with the known tendency on the part of silver to form salts corresponding to the enolic or labile form of tautomeric compounds (for example, benzamide, succinimide), it might be expected that the silver salt of ethyl acetoacetate would possess the OAg structure. As such, since interaction with ethyl iodide results in the formation of the O.C2H, compound in small proportion, it seems difficult to account for the fact that the C.C2H, compound constitutes the main product, unless the simultaneous formation of CAg salt is assumed.

The author has been led to adopt the view that both types of silver salt are capable of formation and interaction simply by double decomposition, not only as affording the simplest explanation of the results obtained, but also because it seems to be in harmony with the state of ethyl acetoacetate as a tautomeric pair in dynamic equilibrium. A somewhat important factor in the consideration of the mechanism of interaction of an agent such as silver oxide and ethyl iodide with a mixture of dynamic isomerides, such as ethyl acetoacetate, is the speed with which the reaction once initiated proceeds. By analogy, it might reasonably be expected that the ease with which oxide of silver interacts with formation of OAg salt would be superior to that with which CAg salt is produced. If the rate of interaction of the ester, oxide, and iodide were slow, time would be allowed for the isomerisation of the ketonic form, so that the reaction would run a course parallel to that with diazomethane. The reaction, on the contrary, is very rapid. Admitting the existence of an affinity between oxide and ether tending to the production of the CAg salt, even were it considerably inferior to that tending to produce the OAg salt, little time is allowed for the ketonic form to undergo the isomerisation necessary for the production of the latter. Traube's observations (loc. cit.) of the rate of change of density in solution of ethyl acetoacetate indicate that comparatively large intervals of time are required for the establishment of the condition of equilibrium. That the state of equilibrium is not very greatly affected either by change of temperature or influence of solvent is shown by Perkin's observations of electromagnetic rotation (Trans., 1892, 61, 808), and by Wislicenus' colorimetric results (Annalen, 1896, 291, 175; Ber., 1899, 32, 2839).

No

By inference from the case of silver, provided the view here expressed be accepted, it might be inferred by analogy that the constitution of the sodium, and possibly also potassium, salts of ethyl acetoacetate, should be represented as belonging to the CM type. stress is laid upon such processes of inference. From the fact that occasionally the sodium salt affords derivatives of both types, it might be argued that sodium salts of both types exist. In the author's opinion, the mode of interaction of the sodio-salt may depend in great

measure upon the mode of its application. Claisen's observation that the interaction of an alcoholic solution of ethyl sodioacetoacetate with ethyl chlorocarbonate leads mainly to the production of ethyl carbonate, suggests the conclusion that the alcoholic solution of sodium salt consists of a mixture in equilibrium of ethyl sodioacetoacetate, alcohol, ethyl acetoacetate, and sodium ethoxide:

CH ̧•C(ONa):CH•CO¿C2H¿ +С2H ̧•OH —

5

In such case, it is not easy to say which form of salt undergoes reaction. Supposing that a CR product should be formed preferentially, temporary formation of CNa salt would account for the ultimate reaction of all the ester in that sense. Nevertheless, it should be mentioned that dry ethyl sodioacetoacetate, although the action of iodine effects the elimination of sodium apparently in the C position, yields both O- and C-derivatives by interaction with ethyl chlorocarbonate, in which case it is also employed in the anhydrous form. A similar case is that of ethyl disodiodiacetosuccinate, which, by the action of iodine on the dry salt, yields ethyl diacetofumarate (Just, loc. cit.; compare Paal and Härtel, loc. cit.), and, under similar conditions, gives ethyl bisbenzoyloxycrotonate by the action of benzoyl chloride (Paal and Härtel). The formation of fumarate occurs, however, only to the extent of 5 to 10 per cent. Were a question of constitution under discussion, a complete answer to the question could only be given by accounting for the whole of the sodium salt used.

The author's thanks are due to Prof. Purdie for much valuable advice given during the course of this work.

UNITED COLLEGE OF ST. SALVATOR AND ST. LEONARD,
ST. ANDREWS.

LXV.-Hydrosulphides, Sulphides, and Polysulphides of Potassium and Sodium.*

By W. POPPLEWELL BLOXAM, B.Sc.

In a paper entitled "The Sulphides and Polysulphides of Ammonium" (Trans., 1895, 67, 277), the author has given a statement of the results of his work in this field. The study of these compounds was continued after publication of this paper, but, owing to experimental difficulties, it was subsequently decided to abandon the further investi

An abstract of a paper communicated to the Chemical Society on June 1, 1899.