FUMARIC AND MALEIC ACIDS

fumaric and maleic acids, two isomeric unsaturated acids of composition c4h4o4. _fumaric acid_ is found in fumitory (_fumaria officinalis_), in various fungi (_agaricus piperatus_, &c.), and in iceland moss. it is obtained by heating malic acid alone to 150 deg. c., or by heating it with hydrochloric acid (v. dessaignes, _jahresb_., 1856, p. 463) or with a large quantity of hydrobromic acids (a. kekule, _ann._, 1864, 130, p. 21). it may also be obtained by boiling monobromsuccinic acid with water; by the action of dichloracetic acid and water on silver malonate (t. komnenos, _ann._, 1883, 218, p. 169); by the cyanide synthesis from acetylene di-iodide; and by heating maleic acid to 210 deg. c. (z. skraup, _monats. f. chemie_, 1891, 12, p. 112). it crystallizes in small prisms or needles, and is practically insoluble in cold water. it sublimes to some extent at about 200 deg. c., being partially converted into maleic anhydride and water, the reaction becoming practically quantitative if dehydrating agents be used. reducing agents (zinc and caustic alkali, hydriodic acid, sodium amalgam, &c.) convert it into succinic acid. bromine converts it into dibromsuccinic acid. potassium permanganate oxidizes it to racemic acid (a. kekule and r. anschutz, _ber._, 1881, 14, p. 713). by long-continued heating with caustic soda at 100 deg. c. it is converted into inactive malic acid. _maleic acid_ is obtained by distilling malic or fumaric acids; by heating fumaric acid with acetyl chloride to 100 deg. c; or by the hydrolysis of trichlorphenomalic acid ([beta]-trichloraceto-acrylic acid) [a. kekule, _ann._, 1884, 223, p. 185]. it crystallizes in monoclinic prisms, which are easily soluble in water, melt at 130 deg.