N-Arylcarbamates

Polymer Matrix Effects. In order to approximate the environment experienced by the arylcarbamate moieties in coatings based on aromatic diisocyanates, we chose to study the photochemistry of alkyl N-arylcarbamates in polymethacrylate (PMMA) and polypropyl-methacrylate (PPMA) films. First, however, 2a and 3a were irradiated in ethyl propionate (a model solvent for PMMA and PPMA) to determine the effect of the solvent polarity (dielectric) on the photolysis of the carbamates. Upon excitation at 280 nm, where the solvent absorbance was negligible, is 0.006 for 2a and 0j) is 0.005 for 3a. These values are significantly smaller... 

Molecular Orbital Description of Arylaminyl Radicals. Aryl-aminyl radicals, as previously discussed, are intermediates in both the photolysis of alkyl N-arylcarbamates (7, 8) and the photolysis of arylamines (18). A simplified mechanism for photolysis of arylamines and alkyl N-arylcarbamates is illustrated in Scheme IV for the general case. An indication of the reactivity of the... 

B, Preparation of S olid Derivatives, such as a)Esters of benzoic acid and nitrobenzoic acids (p331) b)Alkyl N-Arylcarbamates (Phenyl- and a-Naph-thy lure thanes) (p331) and e)Bis (triphenylmethyl) Esters (p332)... 

The kinetics of reaction of O-(A-ary I carbamoyl) be n zop h cn o n c oximes in NaOMe-MeOH to give benzophenone oxime sodium salt and the corresponding methyl N-arylcarbamates have been studied.6 The Hamnett constants pobs = 0.68 and pkl = —1.32 have been estimated for the E cBR process for which 2 governs conversion of the intermediate ArNrC02N=CPh2 to ArN=C=0 and Ph2C=NO. ... 

In contrast to aliphatic amines, aromatic amines hardly react with C02 [21a] because of their poorer basicity. However, in the presence of suitable auxiliary bases (B) (such as amidines or penta-alkylguanidine superbases), carbamate salts (BH)02CNRAr (R = H, alkyl) can be generated in solution, as supported by spectroscopic and reactivity data [29]. It has been shown that even tributylamine may be effective if a suitable alkali metal salt is also present in solution in the latter case, the N-arylcarbamate has been isolated as an alkali salt (Equation 6.3)... 

On the basis of their chemical structure carbamic add esters can be divided into N-alkylcarbamates and N-arylcarbamates. 

N-alkylcarbamates and N-arylcarbamates have with respect to their structural formulae the common feature that in formula R2=H. Their general formula is the... 

With respect to halogen substituents this N-alkylcarbamate group is more similar to the N-aryl-N-alkylcarbamates than to the N-arylcarbamates discussed later. 

Friesen reported as early as 1929 on the herbicidal activity of an N-arylcarbamic acid ester, phenyl urethane, however, its action causing abnormal growth on wheat and oats was utilised for practical purposes only IS years later. 

In the last ten years, patents have been obtained for several new N-arylcarbamate derivatives. However, up to the present they have not actually been introduced into agriculture. 

N-acylated urethanes can be considered as N-arylcarbamates with retarded action. 

For the industrial manufacture of N-arylcarbamates one of the following two methods is generally used ... 

Herbicides are the most widely used type of pesticides, and triazines, N-arylcarbamates, and chlorophenoxy acids are among the most important classes of herbicides. Herbicides are used to control unwanted grasses and weeds in a variety of crops, such as cotton, alfalfa, sunflower, sorghum, rice, and a variety of fruits and vegetables. The following experiment involves the analysis of atra-zine as an example of the triazines, 2,4-D for the chlorophenoxy acid herbicides, and chlorpropham for the carbamates. 

---