Subject carbonyl displacement

Bimolecular reactions of aniline with /V-acyloxy-/V-alkoxyamides are model Sn2 processes in which reactivity is dictated by a transition state that resembles normal Sn2 processes at carbon. Electronic influences of substituents support a non-synchronous process which has strong charge separation at the transition state and which is subject to steric effects around the reactive centre, at the nucleophile but not on the leaving group. The sp3 character of nitrogen and disconnection between the amino group and the amide carbonyl renders these reactions analogous to the displacement of halides in a-haloketones. 

Electrophilic substitution at the anthraquinone ring system is difficult due to deactivation (electron withdrawal) by the carbonyl groups. Although the 1-position in anthraquinone is rather more susceptible to electrophilic attack than is the 2-position, as indicated by jt-electron localisation energies [4], direct sulphonation with oleum produces the 2-sulphonic acid (6.3). The severity of the reaction conditions ensures that the thermodynamically favoured 2-isomer, which is not subject to steric hindrance from an adjacent carbonyl group, is formed. However, the more synthetically useful 1-isomer (6.7) can be obtained by sulphonation of anthraquinone in the presence of a mercury(II) salt (Scheme 6.4). It appears that mercuration first takes place at the 1-position followed by displacement. Some disulphonation occurs, leading to the formation of the 2,6- and 2,7- or the 1,5- and 1,8-disulphonic acids, respectively. Separation of the various compounds can be achieved without too much difficulty. Sulphonation of anthraquinone derivatives is also of some importance. 

The catalysis of hydrolysis of carboxylic acid derivatives by weak bases has not been carefully studied until relatively recently. Koshland reported in 1952 the catalysis of acetyl phosphate hydrolysis by pyridine Bafna and Gold (1953) reported the pyridine-catalyzed hydrolysis of acetic anhydride. A short time later the catalysis of aromatic ester hydrolysis by imidazole was demonstrated (Bender and Turnquest, 1957 a, b Bruice and Schmir, 1957). Since that time a large amount of work has been devoted to the understanding of catalyzed ester reactions. Much of the work in this area has been carried out with the purpose of inquiry into the mode of action of hydrolytic enzymes. These enzymes contain on their backbone weak potential catalytic bases or acids, such as imidazole in the form of histidine, carboxylate in the form of aspartate and glutamate, etc. As a result of the enormous effort put into the study of nucleophilic displacements at the carbonyl carbon, a fair understanding of these reactions has resulted. An excellent review is available for work up to 1960 (Bender, 1960). In addition, this subject has been... 

Fatty adds may be subjected to IR spectroscopy in the free (unesterified) state, bound to glycerol or as the methyl ester derivatives, although an esterified form is to be preferred as a band due to the free carboxyl group between 10 and 11 pm may obscure a number of other important features in the spectra. Most information on the chemical nature of fatty acid derivatives can be obtained when they are in solution and Figure 6.10 illustrates the IR spectmm of soybean oil in carbon tetrachloride solution. The sharp band at 5.75 pm is due to the esterified carbonyl function, which is also responsible for a band at 8.6 pm. With free fatty acids, the first of these bands is displaced to 5.9 pm and there are also broad bands at 3.5 pm and 10.7 pm. c/s-Double bonds give rise to small bands at 3.3 pm and 6.1 pm, that are useful as diagnostic aids and are considered sufficiently distinct for use in quantitative estimations in some circumstances [43,59]. Most of the remaining bands are absorption frequencies of the hydrocarbon chain. 

The formation of carbon-carbon bonds in aromatic systems often takes place by an electrophilic attack on the ring by a carbonium ion or a species with carbonium ion character. The large family of reactions related to Friedel-Crafts reaction are of this type. In aliphatic chemistry carbon electrophiles are more likely to be encountered as carbonyl groups or as such compounds as halides and tosylates, which are subject to nucleophilic displacement. Many examples of these types of reactions have been discussed, particularly in Chapters 1, 2, and 6. There are also some valuable synthetic procedures in which carbon-carbon bond formation results from electrophilic attack by a carbonium ion on an alkene. It is this group of reactions that we will now consider. 

Iridium(I) dithiocarbamate complexes have been the subject of a paper by Duckett and co-workers (1451). Reaction of NaS2CNEt2 with [lr(cod)(p-Cl)]2 gives [lr(S2CNEt2)(cod)] from which a range of carbonyl, phosphine, and phosphite complexes are readily prepared via displacement of the diolefin, some of which exhibit luminescence in fluid solution at room temperature. Benzene solutions of [lr(S2CNEt2) P(OPh)3 2] are unstable and result in slow formation of the ortho-metalated iridium(lll) hydride, [IrH(S2CNEt2) P(0Ph)3 P(0Ph)20CeH4 ] (Eq. 140), characterized by a hydride resonance at 8 -16.02. 

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