Electronic and steric effects of alkyl group on denitrosation of 3-alkyl-1-methyl-1-nitrosothioureas.

A series of 3-alkyl-1-methyl-1-nitrosothioureas with R=CH3, C2H5, cyclo-C6H11 (3), (CH3)2CH (4), C2H5(CH3)CH, and (CH3)3C were synthesized and their rates of acid catalyzed (pH<6.5) denitrosation measured. According to rate measurements in CH3COOD–D2O, the kinetic isotope effect kH:kD is 1.25 for 4. Except 3, a linear plot of logkR⁄kMe for the denitrosation of RNHCSN(NO)CH3 vs. σ* provides ρ*=−0.98 (r=−0.997). The significant factor affecting the rate-determining step of the denitrosation of these N-nitrosothioureas at pH 4.6 is the electronic effect of the substituent at the N3 position.