Acidic cleavage

Obtained synthetically by one of the following processes fusion of sodium ben-zenesulphonate with NaOH to give sodium phenate hydrolysis of chlorobenzene by dilute NaOH at 400 C and 300atm. to give sodium phenate (Dow process) catalytic vapour-phase reaction of steam and chlorobenzene at 500°C (Raschig process) direct oxidation of cumene (isopropylbenzene) to the hydroperoxide, followed by acid cleavage lo propanone and phenol catalytic liquid-phase oxidation of toluene to benzoic acid and then phenol. Where the phenate is formed, phenol is liberated by acidification. 

Can you remember what re action of an alkene would give the same products as the periodic acid cleavage shown here" ... 

Periodic acid cleavage of vicinal diols is often used for analytical purposes as an aid m structure determination By identifying the carbonyl compounds produced the con stitution of the starting diol may be deduced This technique finds its widest application with carbohydrates and will be discussed more fully in Chapter 25... 

Only one site for periodic acid cleavage in methyl a D arabmofuranoside... 

Prior to acid cleavage, the mixture is treated with in a biphasic water—toluene system to convert DC and HHP to DHP. This improvement... 

Physical and Chemical Properties. The (F)- and (Z)-isomers of cinnamaldehyde are both known. (F)-Cinnamaldehyde [14371-10-9] is generally produced commercially and its properties are given in Table 2. Cinnamaldehyde undergoes reactions that are typical of an a,P-unsaturated aromatic aldehyde. Slow oxidation to cinnamic acid is observed upon exposure to air. This process can be accelerated in the presence of transition-metal catalysts such as cobalt acetate (28). Under more vigorous conditions with either nitric or chromic acid, cleavage at the double bond occurs to afford benzoic acid. Epoxidation of cinnamaldehyde via a conjugate addition mechanism is observed upon treatment with a salt of /-butyl hydroperoxide (29). 

Acidic cleavage of the oxirane ring in (210) results in formation of the alkynic aldehyde (211) (68TL4905). 

H2/Pd-C, EtOH, 20°. < -Bromobenzyl carbonates have been developed for use in solid-phase peptide synthesis. An aryl o-bromobenzyl carbonate is stable to acidic cleavage (CF3CO2H) of a /-butyl carbamate a benzyl carbonate is cleaved. 

Alkyldithio carbamates are prepared from the acid chloride (Et N, EtOAc, 0°) and amino acid, either free or as the O-silyl derivatives (70-88% yield). The N- i-propyldithio) carbamate has been used in the protection of proline during peptide synthesis. Alkyldithio carbamates can be cleaved with thiols, NaOH, Ph P/TsOH. They are stable to acid. Cleavage rates are a function of the size of the alkyl group as illustrated in the table below. 

Glycol and o -hydroxy acid cleavage Oxidative decarboxylation Oxidative rearrangement of olefins... 

Trialkyltin substituents are also powerful ipso-directing groups. The overall electronic effects are similar to those in silanes, but the tin substituent is a better electron donor. The electron density at carbon is increased, as is the stabilization of /S-carbocation character. Acidic cleavage of arylstannanes is formulated as an electrophilic aromatic substitution proceeding through an ipso-oriented c-complex. ... 

Greene reported the preparation of monoaza-18-crown-6 (i) in 1972. His approach was direct, involving condensation of N-trityldiethanolamine with tetraethylene glycol ditosylate. Removal of the protecting group could be achieved by acid cleavage. Unfortunately, neither details of the synthesis nor physical properties were included in this report. 

The scope of this reaction was investigated by Djerassi, °° who showed that 4-bromo ketones in the series and 2-bromo ketones in the 5a series give unsaturated 2,4-dinitrophenylhydrazones in 80-90% yield on warming under nitrogen with 1.1 moles of 2,4-dinitrophenylhydrazine in acetic acid. Cleavage with pyruvic acid affords the pure unsaturated ketones in 60-70 % yield. 

Ether, water, phenylboronic acid. Cleavage occurs by transesterification. 

The acid cleavage of the aryl— silicon bond (desilylation), which provides a measure of the reactivity of the aromatic carbon of the bond, has been applied to 2- and 3-thienyl trimethylsilane, It was found that the 2-isomer reacted only 43.5 times faster than the 3-isomer and 5000 times faster than the phenyl compound at 50,2°C in acetic acid containing aqueous sulfuric acid. The results so far are consistent with the relative reactivities of thiophene upon detritia-tion if a linear free-energy relationship between the substituent effect in detritiation and desilylation is assumed, as the p-methyl group activates about 240 (200-300) times in detritiation with aqueous sulfuric acid and about 18 times in desilylation. A direct experimental comparison of the difference between benzene and thiophene in detritiation has not been carried out, but it may be mentioned that even in 80.7% sulfuric acid, benzene is detritiated about 600 times slower than 2-tritiothiophene. The aforementioned consideration makes it probable that under similar conditions the ratio of the rates of detritiation of thiophene and benzene is larger than in the desilylation. A still larger difference in reactivity between the 2-position of thiophene and benzene has been found for acetoxymercuration which... 

Somewhat milder oxidative conditions lead to loss of but one carbon. Periodic acid cleavage of the side chain in 65, leads to the so-called etio acid (66). Reaction with propionic anhydride leads to acylation of the 17-hydroxyl group (67). Possibilities for neighboring group participation severely limit the methods available for activating the acid for esterification. Best results seemed to have been obtained by use of a mixed anhydride from treatment with diphenyl chloro-... 

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