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Magnetic reconnection is a topological rearrangement of magnetic field that converts magnetic energy to plasma energy. Astrophysical flares, from the Earth's magnetosphere to γ-ray bursts and sawtooth crashes in laboratory plasmas, may all be powered by reconnection. Reconnection is essential for dynamos and the large-scale restructuring known as magnetic self-organization. We review reconnection theory and evidence for it. We emphasize recent developments in two-fluid physics, and the experiments, observations, and simulations that verify two-fluid effects. We discuss novel environments such as line-tied, relativistic, and partially ionized plasmas, focusing on mechanisms that make reconnection fast, as observed. Because there is evidence that fast reconnection in astrophysics requires small-scale structure, we briefly introduce how such structure might develop. Several areas merit attention for astrophysical applications: development of a kinetic model of reconnection to enable spectroscopic predictions, better understanding of the interplay between local and global scales, the role of collisionless reconnection in large systems, and the effects of flows, including turbulence.

When n-valeric acid was treated with allyl diethyl phosphite and diethyl azodicarboxylate, allyl valeriate and diethyl N-(diethyl)phosphoryl hydrazodicarboxylate were obtained in good yields. Similarly ethyl benzoate was obtained in a nearly quantitative yield by the reaction of benzoic acid with triethyl phosphite and diethyl azodicarboxylate. The reaction of carboxylic acid with triphenyl phosphine and diethyl azodicarboxylate in the presence of an alcohol resulted in the formation of the corresponding esters of the carboxylic acid, triphenyl phosphine oxide, and diethyl hydrazodicarboxylate.The mechanisms of these reactions are also discussed. diethyl allyl phosphite (1 mol) with diethyl azodicarboxylate (1 mol) was first studied, on the assumption that acyl phosphate, allyl valeriate, and diethyl hydrazodicarboxylate would be formed. However, instead of the expected products, allyl valeriate and diethyl N-(diethyl)phosphoryl hydrazodicarboxylate (I) were obtained in 71% and 77% yields respectively, while about 1 mol of the valeric acid was recovered unchanged (54%).Similarly, the reaction of benzoic acid 4.2) and triethyl phosphite with diethyl azodicarboxylate at room temperature resulted in the formation of ethyl benzoate and diethyl N-(diethyl)-phosphoryl hydrazodicarboxylate in 95% and 95% yields respectively. The results are summarized in Table 1.(1)The reaction can be explained in the following manner. An imidoyl phosphonium salt (II) initially formed is protonated, giving an phosphonium carboxylate (III). This phosphonium carboxylate (III) is then, in turn, decomposed into an ester of carboxylic acid and diethyl N-(diethyl)phosphoryl hydrazodicarboxylate by the migration of the alkyl group to the carboxylate anion (Eq. (2));