# 1911 Encyclopædia Britannica/Succinic Acid

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​SUCCINIC ACID, C$_2$H$_4$(CO$_2$H)$_2$. Two acids corresponding to this empirical formula are known - namely ethylene succinic acid, HO$_2$C·CH$_2$·CH$_2$·CO$_2$H and ethylidene succinic acid CH$_3$·CH(CO$_2$H)$_2$.
Ethylene succinic acid occurs in amber, in various resins and lignites, in fossilized wood, in many members of the natural orders of Papaveraceae and Compositae, in unripe grapes, urine and blood. It is also found in the thymus gland of calves and in the spleen of cattle. It may be prepared by the oxidation of fats and of fatty acids by nitric acid, and is also a product of the fermentation of malic and tartaric acids. It is usually obtained by the distillation of amber, or by the fermentation of calcium malate or ammonium tartrate. Synthetically it may be obtained by reducing malic or tartaric acids with hydriodic acid (R. Schmitt, Ann., 1860, 114, p. 106; V. Dessaignes, ibid., 1860, 115, p. 120; by reducing fumaric and maleic acids with sodium amalgam; by heating bromacetic acid with silver to 130° C.; in small quantity by the oxidation of acetic acid with potassium persulphate (C. Moritz and R. Wolffenstein, Ber., 1899, 32, p. 2534); by the hydrolysis of succinonitrile (from ethylene dibromide) C$_2$H$_4$$\to$C$_2$H$_4$Br$_2$$\to$C$_2$H$_4$(CN)$_2$$\to$C$_2$H$_4$(CO$_2$H)$_2$; by the hydrolysis of β-cyanpropionic ester; and by the condensation of sodiomalonic ester with monochloracetic ester and hydrolysis of the resulting ethane tricarboxylic ester (RO$_2$C)$_2$CH·CH$_2$·CO$_2$R; this method is applicable to the preparation of substituted succinic acids. It is also produced by the electrolysis of a concentrated solution of potassium ethyl malonate.
It crystallizes in prisms or plates which melt at 185° C. and boil at 235° C. with partial conversion into the anhydride. It is readily soluble in water. Aqueous solutions of the acid are decomposed in sunlight by uranium salts, with evolution of carbon dioxide and the formation of propionic acid. Potassium permanganate, in acid solution, oxidizes it to carbon dioxide and water. The sodium salt on distillation with phosphorus trisulphide gives thiophene. The esters of the acid condense readily with aromatic aldehydes and ketones to form γ-disubstituted itaconic acids and γ-alkylen pyrotartaric acids (H. Stobbe, Ann, 1899, 308, p. 71). γ-Oxyacids are formed when aldehydes are heated with sodium succinate and sodium acetate. Numerous salts of the acid are known, the basic ferric salt being occasionally used in quantitative analysis for the separation of iron from aluminium.
Succinyl chloride, obtained by the action of phosphorus pentachloride on succinic acid, is a colourless liquid which boils at 190° C. In many respects it behaves as though it were dichlorbutyro-lactone,$C_{2}H_{4}\left\langle {\begin{matrix}CCl_{2}\\CO\end{matrix}}\right\rangle O$; e.g. on reduction it yields butyro-lactone, and when condensed with benzene in the presence of aluminium chloride it yields chiefly γ-diphenylbutyro-lactone. Succinic anhydride, C$_2$H$_4$(CO)$_2$O, is obtained by heating the acid or its sodium salt with acetic anhydride; by the action of acetyl chloride on the barium salt; by distilling a mixture of succinic acid and succinyl chloride, or by heating succinyl chloride with anhydrous oxalic acid. It crystallizes in plates which melt at 120° C., and distils without decomposition. It is slowly dissolved by water with the formation of the acid. It combines readily with the meta-aminophenols to form rhodamines, which are valuable dyestuffs. Heated in a current of ammonia it gives succinimide, which is also obtained on heating acid ammonium succinate. It crystallizes in colourless octahedra which melt at 125—126° C., and is easily soluble in water. When warmed with baryta water it yields succinamic acid, HO$_2$C·CH$_2$·CH$_2$·CONH$_2$; and with alcoholic ammonia at 100° C. it gives succinamide. The imino hydrogen atom is easily replaced by metals. Distillation with zinc dust gives pyrrol (q.v.). By the action of bromine in alkaline solution it is converted into β-aminopropionic acid. Succinamide, C$_2$H$_4$(CONH$_2$)$_2$, best obtained by the action of ammonia on diethyl succinate, crystallizes in needles which melt at 242—243° C., and is soluble in hot water. Succinonitrile, C$_2$H$_4$(CN)$_2$, is obtained by the action of potassium cyanide on ethylene dibromide or by the electrolysis of a solution of potassium cyanacetate. It is an amorphous solid which melts at 54—55° C. On reduction with sodium in alcoholic solution it yields tetraethylene diamine (putrescein) and pyrollidine.
Methyl succinic acid (pyrotartaric acid), HO$_2$C·CH$_2$·CH·(CH$_3$)·CO$_2$H, is formed by the dry distillation of tartaric acid; by heating pyruvic acid with concentrated hydrochloric acid to 180° C.; by the reduction of citraconic and mesaconic acids with sodium amalgam; and by