Acid chloride, hydrolytic reactivity

It is also possible to prepare them from amino acids by the self-condensation reaction (3.12). The PAs (AABB) can be prepared from diamines and diacids by hydrolytic polymerization [see (3.12)]. The polyamides can also be prepared from other starting materials, such as esters, acid chlorides, isocyanates, silylated amines, and nitrils. The reactive acid chlorides are employed in the synthesis of wholly aromatic polyamides, such as poly(p-phenyleneterephthalamide) in (3.4). The molecular weight distribution (Mw/Mn) of these polymers follows the classical theory of molecular weight distribution and is nearly always in the region of 2. In some cases, such as PA-6,6, chain branching can take place and then the Mw/Mn ratio is higher. 

Perhaps the most interesting finding of our synthetic studies was that the interfacial preparation of poly(iminocarbonates) is possible in spite of the pronounced hydrolytic instability of the cyanate moiety (see Illustrative Procedure 3). Hydrolysis of the chemically reactive monomer is usually a highly undesirable side reaction during interfacial polymerizations. During the preparation of nylons, for example, the hydrolysis of the acid chloride component to an inert carboxylic acid represents a wasteful loss. 

To obtain polyphenyldiethylsiloxane varnishes, it is possible to fill the hydrolyser with a mixture of diethyldichlorosilane and ethyltrichlorosilane instead of ethyl paste. In this case there is no need to add hydrochloric acid to the reactive mixture, since the hydrolytic cocondensation of phenyl paste with ethylchlorosilanes forms hydrogen chloride, which dissolves in water. 

The previous discussion can be used to interpret the hydrolytic behavior of a series of compounds that possess the same acyl group but varied leaving groups. For example, the order of hydrolytic reactivity for an amide, an ester, an anhydride, and an acid chloride is ... 

N -Heterocyclic Sulfanilamides. The parent sulfanilamide is manufactured by the reaction of A/-acetylsulfanilyl chloride with excess concentrated aqueous ammonia, and hydrolysis of the product. Most heterocycHc amines are less reactive, and the condensation with the sulfonyl chloride is usually done in anhydrous media in the presence of an acid-binding agent. Use of anhydrous conditions avoids hydrolytic destmction of the sulfonyl chloride. The solvent and acid-binding functions are commonly filled by pyridine, or by mixtures of pyridine and acetone. Tertiary amines, such as triethylamine, may be substituted for pyridine. The majority of A/ -heterocycHc sulfanilamides are made by simple condensation with A/-acetylsulfanilyl chloride and hydrolysis. 

In contrast to oxidative dechlorination, the hydrolytic dechlorination of chloramphenicol replaces a Cl-atom with a OH group to yield a (monochlo-ro)hydroxyacetamido intermediate. The latter, like the dichloro analogue, also eliminates HC1, but the product is an aldehyde that is far less reactive than the oxamoyl chloride intermediate. Chloramphenicol-aldehyde undergoes the usual biotransformation of aldehydes, namely reduction to the primary alcohol 11.41 and dehydrogenation to the oxamic acid derivative 11.40 (Fig. 11.7). 

Hydrolytic enzymes remain active during CHC13 fumigation (Brookes 1982). Amato and Ladd (1988) showed that the amounts of ninhydrin-reactive compounds (i.e., ammonium, amino acids, peptides, and proteins) released from the biomass during fumigation and extracted by 2 M potassium chloride (KC1) are closely correlated to the initial biomass C concentrations. 

The catalytic regrouping of the products of the hydrolytic condensation of diethyldichlorosilane is conducted in the following way. They are mixed with 15-20% of ethylsiloxane liquid (synthesised by the hydrolysis of the reactive 3 1 mixture of ethyl magnesium chloride and tetraeth-oxysilane and containing mostly hexaethyldisiloxane) and treated with activated kil clay or sulfuric acid (the reaction is similar to the one shown above). 

The mixture is agitated for 10-15 minutes then, chloroethers are sent from batch box 6 through a siphon at such speed that the temperature in the hydrolyser does not exceed 20 3 °C. After all the chloroethers have been introduced, the reactive mixture is kept at the temperature of hydrolytic condensation for 6-8 hours. Most of the hydrogen chloride released during hydrolytic condensation dissolves in water the excess is withdrawn into a water-flushed hydroejector (not shown in the diagram) and in the form of weak hydrochloric acid sent to biochemical purification. 

The temperature of hydrolytic cocondensation (50-70 °C) is regulated by changing the temperature of water and the speed at which the reactive mixture is introduced. The released hydrogen chloride partially dissolves in excess water, and partially is withdrawn through faolite piping into water-flushed hydroejector 9 and in the form of weak hydrochloric acid sent into collector 14. 

The S5mthetic approach of in situ activation of carboxylic acids is based on the preliminary reaction of the carboxylic acid with a specific reagent to give an intermediate reactive daivative which can be prepared prior to the reaction with cellulose or converted directly in a one-pot process. This approach opens the way to a broad variety of new esters, because for numwous acids, for example unsaturated or hydrolytically unstable ones, reactive derivatives such as anhydrides or chlorides simply cannot he synthesized. The mild reaction conditions apphed for the in situ activation prevent common side reactions hke pericychc reactions, hydrolysis, and oxidation. Moreover, due to their hydrophobic charactCT, numa-ous anhydrides are not soluble in organic media used for cellulose modification, resulting in unsatisfactory yields and insoluble products. In addition, the conversion of an anhydride is combined with the loss of half of the acid during the reaction. Consequently, in situ activation is much more efficient. 

In the case of metals and transition metals, condensation occurs around 1(X)°C, bringing out higher activation energies than hydrolytic processes. However, silicon is less reactive tertiary alkyl or benzylic R groups are needed (Corriu, 1994) otherwise, Lewis acids, such as iron or aluminum chloride, are required to catalyze the condensation (Bourget, 1998). As a consequence the reactivities of silicon and metal precursors are expected to be leveled in the preparation of silicates, since the metal species are expected to act as Lewis acid catalysts (see below). 

Satisfactory alternatives to the hydrolytic procedures have been sought for many years. Methods have been tried to produce colored derivatives by exploiting the reactivity of the indole nucleus in the intact protein (135, 353). Sodium hypochlorite, ferric chloride, cupric sulfate, bromine, and sodium nitrite, usually in acid solution, have been found to produce color with tryptophan-containing proteins. Later workers have formed other colored derivatives by reaction with tryptophan-specific reagents, while still others have used the characte-... 

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