Photo-on-Demand In Situ Synthesis of N-Substituted Trichloroacetamides with Tetrachloroethylene and Their Conversions to Ureas, Carbamates, and Polyurethanes

Abstract

N-substituted trichloroacetamides (NTCAs), which serve as blocked isocyanates, were synthesized in ∼97% yields by in situ photo-on-demand trichloroacetylation of amines with tetrachloroethylene (TCE). The reactions were performed by photo-irradiation of TCE solutions containing an amine under O2 bubbling over 70 °C with a low-pressure mercury lamp. TCE underwent photochemical oxidation to afford trichloroacetyl chloride having high toxicity and corrosivity, which then reacts in situ with the amine to afford NTCA. Compared with conventional NTCA synthesis with hexachloroacetone, the present reaction has the advantage of being widely applicable to a variety of amines, even those with low nucleophilicity such as amides, fluorinated amines, and amine HCl salts. NTCAs could be converted to the corresponding N-substituted ureas and carbamates through base-catalyzed condensation with amines and alcohols, respectively, with the elimination of CHCl3. The reaction may proceed by the initial formation of isocyanate and its subsequent addition reaction with the amine or alcohol. This photochemical reaction also enables the synthesis of fluorinated NTCAs, which accelerate the reactions, and realizes the synthesis of novel fluorinated chemicals including polyurethanes.

Photo-on-Demand In Situ One-Pot Synthesis of Carbonate Esters from Tetrachloroethylene

“…This result is consistent with the fact that the ratio of COCl 2 in the photooxidation of TCE increased with increasing temperature as reported previously. 3 In contrast, the reaction was decelerated by increasing the concentration of TFE and pyridine to the ratio of 10:2:3 (entry 4). The reaction barely proceeded upon further increasing TFE and pyridine to the ratio of 10:5:7.5, probably due to the threshold concentration (entry 5).…”

“…Recently, we achieved the direct photochemical conversion of TCE to NTCA with a solution of TCE and amine [Scheme 1, reaction (II)]. 3 The obtained NTCAs could be converted to N-substituted ureas and carbamates via strong base-catalyzed condensation reactions with amines or alcohols. However, to the best of our knowledge, no example has been reported for the synthesis of carbonate esters from TCE via the reaction of TCAE and an alcohol.…”

“…Although the social uses of TCE have included physical recycling by filtration and distillation, its chemical recycling has attracted less attention. Therefore, we have studied the chemical conversion of TCE to valuable organic compounds by safe, simple, inexpensive, and low-environmental-impact organic reactions. , It is known that TCE undergoes photochemical oxidation upon irradiation with UV-C light to give trichloroacetyl chloride (TCAC) and phosgene (COCl 2 ) as major and minor products, respectively [Scheme , reaction I-(path 1)]. − These compounds are highly toxic and corrosive but nevertheless are very important carbonyl sources in organic synthesis. , …”

“…The elimination capability of the CCl 3 group is clearly lower than that of the Cl group. Recently, we achieved the direct photochemical conversion of TCE to NTCA with a solution of TCE and amine [Scheme , reaction (II)] . The obtained NTCAs could be converted to N-substituted ureas and carbamates via strong base-catalyzed condensation reactions with amines or alcohols.…”

Photo-on-Demand In Situ Phosgenation Reactions That Cross Three Phases of a Heterogeneous Solution of Chloroform and Aqueous NaOH

“…The reaction occurred efficiently in a short time upon irradiation of CHCl 3 under O 2 bubbling using UV-C light from a low-pressure mercury lamp (LPML). We then developed photo-on-demand in situ phosgenation reactions for synthesizing a variety of organic chemicals and polymers with CHCl 3 solutions containing both a substrate and an organic base [Scheme , reaction (c)]. − Although alcohols such as EtOH serve to stabilize CHCl 3 , and the organic bases and solvents absorb UV-C light, , the phosgenation products were obtained in high yields through in situ reactions of the substrates and COCl 2 generated from CHCl 3 . These results indicated that the photochemical oxidation of CHCl 3 occurred not only in the liquid phase but also in the gas phase.…”