Oxidative Coupling of Thiols to Disulfides in Solution with Tripropylammonium Halochromates, (C3H7)3NH[CrO3X], (X = F,Cl) Adsorbed on Alumina

A mild and efficient method for the oxidative coupling of thiols by tripropylammonium fluorochromate and tripropylammonium chlorochromate absorbed on alumina in solution is reported. Alumina absorbed tripropylammonium fluorochromate and tripropylammonium chlorochromate are efficient and new reagents, which are easily prepared and oxidize thiols to the corresponding disulfides quickly. The reactions are clean and readily controlled to stop at the disulfide stage without the formation of common over-oxidized side products. Thus the advantages of the easy procedure and work up, short reaction times, and excellent yields make this a viable alternative method.     

N-Methylpiperidinium Chlorochromate Adsorbed on Alumina: A New Deoximation Reagent

Summary.  N-Methylpiperidinium chlorochromate adsorbed on alumina was found to be an efficient and selective reagent for the mild oxidative cleavage of oximes. Received March 1, 2001. Accepted March 22, 2001     

Solid State Deoximation with Clay SupportedAmmonium Chlorochromate: Regenerationof Carbonyl Compounds Using Microwavesin a Solventless System

Summary.  Ammonium chlorochromate adsorbed on montmorillonite K-10 rapidly regenerates carbonyl compounds from their corresponding oximes under microwave irradiation and solvent-free conditions. Received October 11, 1999. Accepted (revised) November 15, 1999     

Oxidation of Alcohols with 4-Aminopyridinium Chlorochromate Supported on Silica Gel

Summary. 4-Aminopyridinium chlorochromate supported on silica gel was found to be an efficient reagent for the oxidation of primary and secondary alcohols to the corresponding carbonyl compounds.     

Ethylenebis(N‐Methylimidazolium) Chlorochromate (EBMICC): A New Selective and Mild Reagent for Oxidation of Alcohols,Hydroquinones and Trimethylsilyl Ethers

The ethylenebis(N‐methylimidazolium) chlorochromate was prepared by addition of N‐methylimidazole to 1,2‐dibromoethane to form the corresponding dibromide salt and subsequent treatment of this salt with CrO₃ in 6N HCl solution. It is a stable yellow‐orange solid which selectively oxidized benzylic and allylic alcohols, hydroquinones and trimethylsilyl ethers in refluxing acetonitrile. Oxidation of alcohols was also examined under solvent‐free conditions and showed much better yields of the corresponding carbonyls in a very short reaction time when compared with the conventional method.     

Synthesis of 1,3‐Dihydro‐3‐oxo‐2‐benzofuran‐1‐carboxylates via Intramolecular Cyclization of 2‐[2‐(Dimethoxymethyl)phenyl]‐ 2‐hydroxyalkanoates Followed by Oxidation

A novel and efficient method for the preparation of 1,3‐dihydro‐3‐oxo‐2‐benzofuran‐1‐carboxylates 4 under mild conditions has been developed. Thus, the reaction of [2‐(dimethoxymethyl)phenyl]lithiums, generated easily from 1‐bromo‐2‐(dimethoxymethyl)benzenes 1 , with α‐keto esters gives the corresponding 2‐[2‐(dimethoxymethyl)phenyl]‐2‐hydroxyalkanoates 2 . The TsOH‐catalyzed cyclization of these hydroxy acetals is followed by the oxidation of the resulting cyclic acetals 3 with PCC to give the desired products in satisfactory yields. The reaction of [2‐(dimethoxymethyl)‐4,5‐dimethoxyphenyl]lithium with (MeOC?O)₂, followed by treatment with NaBH₄ or organolithiums, affords 2‐[2‐(dimethoxymethyl)‐4,5‐dimethoxyphenyl]‐2‐hydroxyalkanoates 6 , which can similarly be transformed into the corresponding 1,3‐dihydro‐3‐oxo‐2‐benzofuran‐1‐carboxylates 7 in reasonable yields.     

The Role of Oxygen in the Degradation of Methylammonium Lead Trihalide Perovskite Photoactive Layers

In this paper we report on the influence of light and oxygen on the stability of CH₃NH₃PbI₃ perovskite‐based photoactive layers. When exposed to both light and dry air the mp‐Al₂O₃/CH₃NH₃PbI₃ photoactive layers rapidly decompose yielding methylamine, PbI₂, and I₂ as products. We show that this degradation is initiated by the reaction of superoxide (O₂^?) with the methylammonium moiety of the perovskite absorber. Fluorescent molecular probe studies indicate that the O₂^? species is generated by the reaction of photoexcited electrons in the perovskite and molecular oxygen. We show that the yield of O₂^? generation is significantly reduced when the mp‐Al₂O₃ film is replaced with an mp‐TiO₂ electron extraction and transport layer. The present findings suggest that replacing the methylammonium component in CH₃NH₃PbI₃ to a species without acid protons could improve tolerance to oxygen and enhance stability.