Amides, from acid derivatives polarity

Hlectronically, we find that strongly polarized acyl compounds react more readily than less polar ones. I hus, add chlorides are the most reactive because the electronegative chlorine atom withdraws electrons from the carbonyl carbon, whereas amides are the least reactive. Although subtle, electrostatic potential maps of various carboxylic acid derivatives indicate the differences by the relative blueness on the C=0 carbons. Acyl phosphates are hard to place on this scale because they are not used in the laboratory, but in biological systems they appear to be somewhat more reactive than thioesters. 

It is important to reiterate that tertiary amines do not give amides upon reaction with acid derivatives. It is also important to single out two simple amides that are particularly useful formamide (105) and AT,N-dimethylformamide (106 commonly known as DMF). Both are amides derived from formic acid and both are very useful as polar solvents in a variety of reactions. The amide DMF is used as a solvent in many reactions, particularly for the Sn2 reactions in Chapter 11. 

Based on lysine as before, single chain derivatives (18) and bicatenar compounds (19) have been prepared by a strategy the inverse of that described earlier [46]. The products (18 and 19) are obtained with higher overall yields than 17. As before, no protection or deprotection steps are needed in this case [46,47]. The synthesis consists of a reaction between two moduU prepared beforehand, one representing the polar head group in the final product and the other the junction modulus. The preparation of this intermediate starts from aldoses or acids derived Irom them that are coupled with lysine in its basic form (Scheme 15). The yields for this step are quantitative. A subsequent amidation reaction with a hydrogenated or perfluorinated fatty acid (Scheme 16) leads to the monosubstituted compounds (18). Esterification of the free acid function of lysine (Scheme 17) yields in a final step the bicatenar structures (19). 

Amides derived from carboxylic acids (8-144) and the corresponding JV-substituted (8-145) and JV,JV-disubstituted amides (8-146) are polar compounds of low volatility, yet some of them may participate in the aroma of non-acidic foods. Commonly occurring compounds are mainly amides derived from formic and acetic acids. For example, beer contains hundredths to tenths mg/kg JV-methylformamide (8-145, R= H, RY CHj), JV-methylacetamide (8-145, R = rY CHj), JV ,Y-dimethylacetamide (8-146, R= R = R = CHj), JV -(2-methylbutyl)acetamide,whereR= CH3,R = CHjCH (CHj) CH2CH3, its isomer JV-(3-methylbutyl)acetamide, R = CH2 CH2CH(CHj)2 and JV -(2-phenylethyl)acetamide (8-147), which are produced by condensation of carboxylic acids with amines followed by decarboxylation (Figure 8.70). Many non-volatile JV-substituted formamides and acetamides are also produced in the Maillard reaction. Decarboxylation of asparagine catalysed by decarboxylases yields 3-aminopropionamide (8-148), which may become a precursor of acrylamide (see Section 12.2.2). 

Abstract This presentation is a brief review on the resnlts of our work on iodine interaction with thioamides, selenoamides and amides. The thioamides, benzothia-zole-2-thione (BZT) (1), 6-n-propyl-2-thiouracil (PTU) (2), 5-chloro-2-mercap-tobenzothiazole (CMBZT) (3), N-methyl-benzothiazole-2-thione (NMBZT) (4), benzimidazole-2-thione (BZIM) (5), thiazolidine-2-thione (TZD) (6), 2-mercapto-pyridine (PYSH) (7), 2-mercapto-nicotinic acid (MNA) (8), 2-mercapto-benzoic acid (MBA) (9) and 2-mercapto-pyrimidine (PMT) (10) react with producing three type of complexes of formulae [(HL)IJ(l2) (HL= thioamide and n= 0, 1), [(HL) [I3 ] and [(HL-L)]+[l3 ]. The interaction of seleno-amides, derived from, 6-n-propyl-2-thiouracil (RSelJ) (R= Me- (11), Et- (12), n-Pr- (13) and i-Pr- (14)) with I, have also been studied and produced the complexes [(RSeU)IJ of spoke structure. These complexes are stable in non-polar solvents, but they decompose in polar solvents, producing dimeric diselenide compounds or undertake deselenation. 

Lyotropic liquid crystalline properties were observed for poly (arylamide) monodendrons derived from 1,3,5-substituted amino acid chloride hydrochlorides according to Kim [168]. These systems aggregate readily to form high molecular weight species in the absence of complexing ions. Amide solvents containing more than 40 wt.% of the dendrons exhibit nematic phase liquid crystalline texture under a polarizing microscope, whereas, 60 wt.% solutions produce a hard gel under static conditions. 

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