The kinetics of cyclization of substituted phenyl N-(2-hydroxybenzyl)carbamates and their N-methyl analogs, prepared by the reaction of 2-(aminomethyl)phenols with substituted phenyl chloroformates, was studied in dioxane or toluene at the temperatures 110-180 °C. Electron-withdrawing substituents in the leaving phenoxy group strongly accelerate the rate of cyclization (ρ = 2.45 ± 0.15) while the substituents in the other ring have virtually no effect. The cyclization was catalyzed with triethylamine in toluene but not in dioxane. On the basis of these results, the most convenient method for preparation of substituted 4H-1,3-benzoxazin-2(3H)-ones was a one-hour reflux of substituted 4-nitrophenyl N-(2-hydroxybenzyl)carbamates in dioxane. Based on the influence of substituents, solvents (dioxane and toluene) and triethylamine, the reaction mechanism and structure of the transition state were proposed.

The 17O NMR spectra of 17O isotope‐enriched 1,3,5‐trinitrobenzene and its Meisenheimer adducts with hydride ion (1), acetone anion (2) and methoxide ion (3) were measured. The adducts 1–3 show 17O signals shifted upfield compared with those of 1,3,5‐trinitrobenzene. A higher upfield shift is exhibited by the oxygen atoms of the 4‐nitro group (∼90 ppm) and a lower shift by those of the 2‐ and 6‐nitro groups (∼40 ppm). The shift is practically independent of the structure or bulkiness of the nucleophile bound at the tetrahedral centre C1 in the adduct and also, within an experimental error, of the counter ion and solvent (acetonitrile or a mixture of DMSO‐d6 and methanol). The measured δ(17O) values indicate that in the Meisenheimer adducts the negative charge at the oxygen atoms is larger in 4‐NO2 than in 2‐ and 6‐NO2 groups. Copyright © 2000 John Wiley & Sons, Ltd.

S-Acyl-1-phenylthioureas and their 3-methyl derivatives are rearranged to 1-acyl derivatives of thiourea in methanolic solution. The rearrangement of the 1-acyl-1-phenyl derivative to the thermodynamically more stable 3-acyl derivative is subject to specific base catalysis. The rearrangement of acetyl group is about 2 orders of magnitude slower than that of benzoyl group. 1-Acetyl-l-phenylthiourea undergoes base-catalyzed methanolysis (giving phenylthiourea and methyl acetate) instead of the rearrangement. The methanolysis rates of l-acyl-3-phenylthioureas and their N-methyl derivatives have been measured. The acetylthioureas react at most 3x faster than the benzoyl derivatives. The methyl group at the nitrogen adjacent to acyl group accelerates the solvolysis by almost 2 orders of magnitude; the methyl group at the other nitrogen atom retards the solvolysis by almost 1 order of magnitude. Replacement of hydrogen atom by methyl group at the phenyl-substituted nitrogen increases acidity of the phenylacetylthiourea by 2 orders of magnitude. The same replacement at the benzoyl-substituted nitrogen increases the acidity by 3 orders of magnitude, the increase in the case of the acetyl derivative being as large as 4 orders of magnitude.

Base catalyzed cyclization rates have been measured of 22 derivatives of hydantoic and thiohydantoic acid esters in water and methanol. The cyclization of methyl and ethyl esters of hydantoic and 5-methylhydantoic acids is accompanied by hydrolysis of the ester group, whereas with the other derivatives the hydrolysis does not take place. Hydrolysis of the cyclization products (hydantoin and thiohydantoin derivatives) is not significant under the kinetic conditions. The cyclization of methyl ester of 5-phenylhydantoic acid in methanol is reversible; the equilibrium mixture contains 30% of the starting ester. In all the cases the cyclization is subject to specific base catalysis; exceptions are esters of 5-phenylthiohydantoic and 5-phenyl-2-methylthiohydantoic acids whose cyclizations are subject to general base catalysis. Substituents always accelerate the cyclization. The 3-substituents have the greatest effects, the cyclization rate being considerably increased with bulk of the substituents; similarly large effect of 5-phenyl group consists mainly in its polar effects on the pre-equilibrium. The cyclization are slower in methanol at the same concentration of the lyate ion: the greatest difference (up to 3 orders of magnitude) is observed with the 5-phenyl derivatives.

Dissociation constants of nine m- and p-substituted phenylthioureas, 4-nitrophenylurea, and 1-(4-nitrophenyl)-3,3-dimethylurea have been measured in water and in methanol. The pKa values in methanol are higher than those in water by about 4 units. The Hammett ρ constant has the values 2.6 and 2.35 in water and in methanol, respectively. The pKa difference between 4-nitrophenylurea and 4-nitrophenylthiourea is 2.85 in methanol and 3.25 in water.