Polar non-protic solvents

So far as actual changes of mechanistic pathway with change of solvent are concerned, increase in solvent polarity and ion-solvating ability may (but not necessarily will) change the reaction mode from SN2— SN1. Transfer from hydroxylic to polar, non-protic solvents (e.g. DMSO) can, and often do, change the reaction mode from SN1 — Sn2 by enormously increasing the effectiveness of the nucleophile in the system. 

Finally, in the presence of halide salts (bromide or chloride, which in low polarity non-protic solvents bind to Br2 to give a stable trihalide species), the addition reaction proceeds through a rate- and product-determining nucleophilic attack of Br anion on the 1 1 it complex, Scheme 2 path c. No intermediate is formed in this latter reaction the nucleophilic attack of halide (X ) and the Br-Br bond breaking are indeed concerted, although not necessarily synchronous. 

For such reasons, the following section considers in more detail some of the most significant results obtained by our team on the epoxidation with TBHP of unsaturated FAMEs over mesoporous titanium-grafted silicates. In these examples, the epoxidation tests were carried out either in ethyl acetate, which could be even obtained, in principle, from renewable sources and which is relatively less harmful than other polar non-protic solvents, or under solvent-free conditions. 

Plane trigonal hybridisation, 5 Polarisability, 24, 96 Polarisation, 22, 29 Polarised complexes, 108,141, 144 Polar non-protic solvents, 81 Polyenes... 

Figure 3.54 Energy levels of a dipolar, hydrogen bonding molecule M (excited state M ) in a polar, non-protic solvent (left) and a polar, protic solvent (right). H is the H-bond energy in the ground state, H in the excited state. (1), (2), (4) and (7) correspond to solvation relaxation, (3) and (6) to anti-H-bond dissociation, and (5) and (8) to H-bond formation...

Sulphonyl azides are decomposed by Fe2(CO)g at room temperature or by Fe(CO)5 at 80° in non-polar non-protic solvents such as benzene or cyclohexane to give novel stable complexes having the probable structure (406) (or the cyclic dimer) in which all the carbonyl groups on iron have been displaced . 

The IMI OMC production process involves two main chemical transformations (Scheme 3) [24]-bromination of commercial anisole produces p-bromoanisole (p-BA) with para-regioselectivity > 97 %. Heterogeneous Heck coupling between the p-BA and commercially available octyl acrylate (OA), in the presence of a Pd/C catalyst, with Na2C03 as HBr sponge, and A-methylpyrrolidone (NMP) as the polar, non-protic solvent, furnishes OMC. 

The use of Heck technology at IMI has enabled the preparation of the same acid in either one step (in an aqueous medium) or two steps (in a polar non-protic solvent) (Scheme 6) [28]. The p-fluoroalkylmethacrylate conversion stage involves an unusual 1,3-hydrogen shift. 

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