THE CHEMISTRY OF FORMIC ACID AND ITS SIMPLE DERIVATIVES HARRY W. GIBSON Chemicals and Plastics Division, Union Carbide Corporation, Tarrytown, New York 10591 Received January 27, 1969 Contents i. ii. HI. IV. v. VI. VU. Introduction Formic Acid and Its Salts A. Physical Properties B. Chemical Properties 1. Structure 2. Reaction as an Acid 3. Decomposition Reactions 4. Formic Acid as a Reducing Agent 5. Solvolysis Reactions 6. Free-Radical Reactions Formic Anhydrides and Formyl Halides Formate Esters A. Physical Properties B. Chemical Properties 1. Electrophilic Reactions 2. Decomposition Reactions 3. Free-Radical Reactions Formamide A. Physical Properties B. Chemical Properties 1. Nucleophilic Reactions 2. Electrophilic Reactions 3. Free-Radical Reactions 4. Decomposition Reactions Monosubstituted Formamides A. Physical Properties B. Chemical Properties 1. Nucleophilic Reactions 2. Electrophilic Reactions 3. Free-Radical Reactions 4. Decomposition Reactions Disubstituted Formamides 673 673 673 673 673 674 677 678 681 682 682 683 683 683 683 684 685 686 686 686 686 688 688 689 690 690 690 690 691 692 692 692 I. Introduction Although formic acid and its salts, simple esters, and amides are among the earliest known organic chemicals, no major re- view of their chemistry has appeared in the technical litera- ture. This is in contrast to the closely related formaldehyde, which has been extensively reviewed. This article is an attempt to review the literature on formic acid and its simple salts, esters, and amides through 1966. Chemical Abstracts was searched under the following head- ings: formic acid, formates, and formamide. Many more re- cent references are included, but no attempt was made to ex- haustively search the literature after December 1966. This review is not an in-depth compilation of all the ex- amples of each reaction (an almost insurmountable task). Rather, it is meant to convey the scope (breadth) of reactivity of these compounds and to stimulate interest in some of their unique properties. Thus, only references of primary interest are included. II. Formic Acid and Its Salts HCOOH HCOO- 1 2 A. PHYSICAL PROPERTIES Formic acid is a colorless liquid which freezes at 8.4° and boils at 101°. The dielectric constant is 58. It has a sharp pun- gent odor and is miscible in all proportions with water. Formic acid tends to form azeotropes and a variety of these are known. 1 Among the more interesting are those containing tertiary ammonium formates 2-6 which, as shall be seen, have some interesting properties. Formic acid exhibits severe toxicity as both an acute (short duration) local and acute systemic hazard. 7 It shows slight chronic (long duration) systemic toxicity and moderate chronic local toxicity. 7 Thus, exposure to skin, ingestion, and inhala- tion should be avoided. B. CHEMICAL PROPERTIES 1. Structure The aldehyde-like reducing properties of formic acid (see sec- tion II.B.4) encouraged some early chemists to postulate that formic acid is abnormal in structure. 8-10 More modern tech- niques have shown this not to be the case, 11 ' 12 except that the ether C-O bond is abnormally short, indicating much double- bond character. 13 This undoubtedly contributes to its rela- tively high acidity. (1) "Azeotropic Data," Advances in Chemistry Series, American Chemical Society, Washington, D. C , 1952, p 23. (2) E. J. Poziomek and M. D. Pankau, J. Chem. Eng. Data, 8, 627 (1963). (3) M. Sekiya and K. Ito, Chem. Pharm. Bull. (Tokyo), 12,677 (1964). (4) M. Sekiya, K. Ito, A. Hara, and J. Suzuki, ibid., 15, 802 (1967). (5) M. Sekiya, Y. Harada, and K. Tanaka, ibid., 15,833 (1967). (6) Farbenfab. Bayer A.-G., Netherlands Patent 6,503,120 (1965); Chem. Abstr., 64, 6501 (1966). (7) N. I. Sax, "Dangerous Properties of Industrial Materials," 2nd ed, Reinhold Publishing Corp., New York, N. Y., 1965. (8) M. Prud'homme, /. Chim. Phys., 16, 438 (1918). (9) R. M. Halasyam, Current Set, 4, 812 (1936); Chem. Abstr., 30, 5557 (1936). (10) T. L. Davis and W. P. Green, Jr., J. Amer. Chem. Soc, 62, 1274 (1940). (11) R. M. Halasyam, /. Indian Chem. Soc., 12, 813 (1935); Chem. Abstr., 30,4149 (1936). (12) P. B. Sarkar and B. C. Ray, Nature, 137,495 (1936). (13) R. G. Lerner, J. P. Friend, and H. P. Dailey, /. Chem. Phys., 23, 210(1955). 673