organic compounds that contain an atom of arsenic directly bonded to a carbon atom. The most important types of organoarsenic compounds that contain trivalent arsenic are as follows.
(1) Primary arsines, RAsH2; secondary arsines, R2AsH; and tertiary arsines, R3As.
(2) Haloarsines, RAsX2 and R2AsX (X is a halogen atom).
(3) Oxides and acids, RAsO, RAs (OH)2, and R2As (OH).
(4) Diarsines, such as tetramethyldiarsine (dicacodyl), (CH3)2As—As (CH3)2.
(5) Polyarsines, (—RAs—)x.
(6) Arsenobenzenes, Ar—As=As—Ar.
The known pentavalent arsenic compounds include halides, Rn AsX5 - n; arsenic acid derivatives of the formula RAsO(OH)2, R2AsO (OH), R3AsO, and R4AsOH; and pentaphenyl arsenic, (C6H5)5As. Arsenic ylides, Ar3As+—CR2, constitute a special class of compounds. Organoarsenic compounds are sometimes incorrectly defined as including esters of arsenous and arsenic acids, (RO)3As and (RO)3AsO, which do not contain the As—C bond.
Various methods are used to isolate organoarsenic compounds. The most important methods are the following.
(1) The action of organometallic compounds on arsenic halides:
3RMgX + AsX3→R3As + 3MgX2
(2) The action of alkylating agents on arsenous acid salts (the Meyer reaction):
CH3I + (NaO)3As→CH3As (O)(ONa)2 + Nal
(3) The condensation of arsenic halides with aromatic or unsaturated compounds:
(4) The interaction of diazonium salts with arsenous acid salts (the Bart reaction):
C6H5N2+X- + (NaO)3As→C6H5As (O)(ONa)2 + NaX + N2
(5) The interaction of arylazocarboxylic acids with arsenic halides (the Nesmeianov reaction).
Many organoarsenic compounds are physiologically active. For example, Salvarsan (discovered by P. Ehrlich in 1909) was the first synthetic chemotherapeutic preparation and has been used successfully in the treatment of syphilis. Organoarsenic compounds such as adamsite and lewisite were used as agents of chemical warfare during World War I (1914–18).