Carbonyl substitution reactions

The general chemistry of acylpyridinium salts (181) and their role in the nucleophilic catalysis by pyridine of carbonyl substitution reactions have been reviewed and compared with the role of acylammonium salts (182). ... 

The pentacarbonylmanganese halides have been known for some time1 2 but are still the subject of intense interest. Numerous vibrational analyses h- ve been carried out,3 as well as synthetic and kinetic studies of carbonyl substitution reactions.4 Halide substitution, which requires elevated temperatures,5 leads to charged species. Diazocyclopentadienes insert into the manganese-halogen bond.6... 

The complex Mn2(/x-H)(/x-PPh2)(CO)8 undergoes carbonyl substitution reactions with phosphite, phosphine, or isocyanide ligands, either thermally or... 

This hydrolysis reaction can V I be considered the reverse of the carbonyl substitution reaction carboxylic acid + alcohol —> ester + water. 

Photochemical reactions have been used for the preparation of various olefin, and acetylene complexes (7). Application to the coordination of dienes as ligands has not been used extensively, so far. In this article the preparative aspects of the photochemistry of carbonyls of the group 6 and group 7 elements and some key derivatives, with the exception of technetium, with conjugated and cumulated dienes will be described. Not only carbonyl substitution reactions by the dienes, but also C—C bond formation, C—H activation, C—H cleavage, and isomerizations due to H shifts, have been observed, thereby leading to various types of complexes. 

The lower the pkTaH, the better the leaving group in carbonyl substitution reactions. 

Now for some of the reactions you have seen in the last few chapters. Starting with carbonyl substitution reactions, the first example is the conversion of acid chlorides into esters. The simplest mechanism to understand is that involved when the anion of an alcohol (a metal alkoxide RO ) reacts with an acid chloride. The kinetics are bimolecular rate = fc[MeCOCl] [RO ]. The mechanism is the simple addition elimination process with a tetrahedral intermediate. 

The unimolecular mechanism is unusual for carbonyl substitution reactions. Those in the last chapter as well as the carbonyl addition reactions in Chapter 6 all had nucleophilic addition to the carbonyl group as the rate-determining step. An example would be the formation of an ester from an anhydride instead of from an acid chloride. 

In Chapter 12 pyridine was often used as a catalyst in carbonyl substitution reactions. It can act in two ways. In making esters from acid chlorides or anhydrides pyridine can act as a nucleophile as well as a convenient solvent. It is a better nucleophile than the alcohol and this nucleophilic catalysis is discussed in Chapter 12 (p. 282). But nonnucleophilic bases also catalyse these reactions. For example, acetate ion catalyses ester formation from acetic anhydride and alcohols. 

Thefactthatthia is an /V,/V ftnethyl -amide should remind you of the use of this kind of saturated amide id carbonyl substitution reactions with RU In Chapter 12. 

These too are made by carbonyl substitution reactions, but this time the nucleophile is aromatic and the electrophile is an aliphatic derivative of carbonic acid such as phosgene (COCI2) or a carbonate diester [CO(OR)2]. The aromatic nucleophile is a diphenol but the two OH groups are on separate rings joined together by an electrophilic aromatic substitution. This compound is called bisphenol A and has many other applications. 

Co-polymerization of pentaerythritol and two other monomers—an unsaturated acid and benzene 1,3-dicarboxylic acid—gives a network of polymer chains branching out from the quaternary carbon atom at the centre of pentaerythritol. The reaction is simply ester formation by a carbonyl substitution reaction at high temperature (> 200°C). Ester formation between acids and alcohols is an equilibrium reaction but at high temperatures water is lost as steam and the equilibrium is driven over to the right. 

A trans effect see Trans Effect) in octahedral metal-carbonyl substitution reactions was observed in the reactions of Cr(CO)4TU with CO ... 

Reactions with metal carbonyls Substitution reactions Ring expansion reactions... 

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