Substitued acids

Pyrroles are hydrogenated with more difficulty than are carbocyclic aromatics. In compounds containing both rings, hydrogenation will proceed nonselectively or with preference for the carbocyclic ring (/9), unless reduction of the carbocyclic ring is impeded by substituents. Acidic solvents are frequently used but are not necessary. 

Carboxylic acids can be transformed into a variety of carboxylic acid derivatives in which the carboxyl -OH group has been replaced by another substituent. Acid halides, acid anhydrides, esters, and amides arc the most common such derivatives in the laboratory thioesters and acyl phosphates are common in biological molecules. 

Recent studies have found enhanced substituent solvation assisted resonance effects in dipolar non-hydrogen bonding solvents131. For several +R substituents acidities of phenols in DMSO are well correlated with their gas-phase acidities. The substituents include m- and p-SOMe, m- and p-S02Me, m-S02CF3 and m-N02. But there is very considerable enhancement of the effect of p-S02CF3, p-N02 and various other para-substituents in DMSO solution. 

Selective reductions. Brown et al.2 conducted an extensive study of reductions with diborane in THF. Most aldehydes and ketones are readily reduced unusually high stereoselectivity was realized in the case of norcamphor, which was reduced to 98% endo-norbornanol and 2% exo-norbornanol. p-Benzoquinone is reduced to hydroquinone at a moderate rate, but reduction of anthraquinone is sluggish. Carboxylic acids are reduced very rapidly indeed this group can be reduced selectively in the presence of many other substituents. Acid chlorides react much more slowly than carboxylic acids. Esters and ketones are reduced relatively slowly. Reactions with epoxides are relatively slow and complex. 

Certain sample groups i have been excluded from the plots of Fig. 10-10 because they merit special attention. These include olefinic or aromatic carbon atoms (—CH=), halogen substituents, acids, and moderately strong bases (pKj, < 5). The preferential adsorption of olefins and aromatic hydrocarbons on magnesia has already been noted (Section 7-3B). It is of interest to compare the values of an unsaturated carbon group (—CH=) for the different adsorbents with values calculated from Fig. 

Benzene Substituent Acidic medium Alkaline medium ... 

Substituents Acid system Temp. °C Chemical shifts (ppm) of substituent or ring (in parentheses) protons Standard Ref. 

Substituents Acid system Temp. °C Chemical shifts Standard Ref. 

The oxo(salen)Mn(V) complex, (8) is the effective oxidant in the Mn(III)salen-catalysed oxidation of aryl phenyl sulfides by hypochlorite in MeCN/H20. First-order dependence on oxidant and sulfide is observed and the rate is reduced by electron-attracting substituents in the sulfides and electron-releasing substituents in salen. The Hammett p-value (-2.16.) determined for substituted sulfides indicates an electron-deficient transition state Hammett correlations for substituted salen complexes give positive /O-values for each sulfide. The substituent-, acid-, and solvent effects indicated direct transfer of the 0-atom from the oxidant to the substrate in the rate-determining step. ... 

Kilgore UJ, Roberts JAS, Pool DH, Appel AM, Stewart MP, Dubois MR, Dougherty WG, Kassel WS, Bullock RM, Dubois DL (2011) [Ni(PPh2NC6H4X2)2f Complexes as electrocatalysts Pot H2 production effect of substituents, acids, and water on catalytic rates. J Am Chem Soc 133 5861-5872... 

E amidon transform hydrophobique Granular starch can be chemically modified by substitution of the hydroxyl groups with hydrophobic substituents in the usual way as esters and ethers. The substituent acid anhydrides or halogen-ides and epoxides are containing usually allQrl, aryl- and aralkyl-groups with 8 or 10 or more C-atoms ... 

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