Safety Case Study. Intrinsic Instability of Concentrated Solutions of Alcoholic Hydrogen Chloride: Potential Hazards Associated with Methanol

Advancements in hydrochlorination of alkenes

The hydrochlorination of alkenes has been extensively studied in research and is commonly featured in organic chemistry textbooks as an exemplification of the Markovnikov rule. However, the application of this reaction is typically limited to specific alkenes, such as highly substituted ones, styrenes, or strained systems. Conversely, monosubstituted or 1,2-disubstituted alkenes do not readily react with HCl gas or solutions of HCl gas at practical rates. The challenges associated with hydrochlorination reactions for these "non-activated" alkenes have spurred considerable research efforts over the past 30 years, which constitute the primary focus of this review. The discussion begins with classical polar hydrochlorinations, followed by metal-promoted radical hydrochlorinations, and concludes with a brief overview of recent anti-Markovnikov hydrochlorinations.

Promotion of Water as Solvent in Amination of 4-Chloropyrrolopyrimidines and Related Heterocycles under Acidic Conditions

A switch of reaction medium from organic solvents to water can improve the safety and lower the cost of production processes. Hydrochloric acid-promoted amination of fused pyrimidines has been studied using 4-chloro-7H-pyrrolo[2,3-d]pyrimidine and aniline as model compounds. Higher rate was observed in water than in four alcoholic solvents and DMF. An important aspect is that the amount of acid should be kept low to minimize the competing solvolysis. The substrate scope for the amination in water was evaluated by reacting 4-chloro-7H-pyrrolo[2,3-d]pyrimidine with 20 aniline derivatives with variance in steric and electronic properties. Preparative useful reactions were seen for 14 of the 20 derivatives. Unsuited nucleophiles are ortho-substituted anilines with a pKa below 1. Amination of the corresponding quinazoline, thienopyrimidine, and purine also proceeded well in water. Highly lipophilic and crystalline compounds are more efficiently aminated in 2-propanol. Aliphatic and benzylic amines react poorly under acidic conditions, but these aminations can be done in water without acid.

Palladium-catalyzed regiodivergent hydrochlorocarbonylation of alkenes for formation of acid chlorides

Novel strategy for acid chlorides formation that do not use carboxylic acids is particularly attractive in chemical synthesis but remains challenging. Herein, we reported the development of a highly effective Pd-catalyzed hydrochlorocarbonylation of alkenes with CO for the formation of alkyl acid chlorides. Chlorosilane and AcOH were found as a mild HCl source for the reaction. The reaction shows broad substrate scope and produces both branched and linear alkyl acid chlorides in good to high yields upon different ligands and solvents. Cooperating with follow-up acylation reactions, the Pd-catalyzed hydrochlorocarbonylation offers a complementary platform for the synthesis of diverse carbonyl compounds from alkenes. Mechanistic investigations suggested that the reaction proceeded though a palladium hydride pathway, and CO prompted reductive elimination of the acyl-Pd-Cl intermediate.