Acid or Alkaline Hydrolysis

The deterruination of amino acids in proteins requires pretreatment by either acid or alkaline hydrolysis. However, L-tryptophan is decomposed by acid, and the racemi2ation of several amino acids takes place during alkaline hydrolysis. Moreover, it is very difficult to confirm the presence of cysteine in either case. The use of methanesulfonic acid (18) and mercaptoethanesulfonic acid (19) as the protein hydroly2ing reagent to prevent decomposition of L-tryptophan and L-cysteine is recommended. En2ymatic hydrolysis of proteins has been studied (20). 

Sulfaguanidine is prepared by condensation of Ai-acetylsulfanilyl chloride with guanidine ia presence of alkali. The A/ -acetyl group is removed by acid or alkaline hydrolysis. 

Enzyme Sta.bihty, Loss of enzyme-catalytic activity may be caused by physical denaturation, eg, high temperature, drying/freezing, etc or by chemical denaturation, eg, acidic or alkaline hydrolysis, proteolysis, oxidation, denaturants such as surfactants or solvents, etc. pH has a strong influence on enzyme stabiHty, and must be adjusted to a range suitable for the particular enzyme. If the enzyme is not sufficiendy stable in aqueous solution, it can be stabilized by certain additives a comprehensive treatment with additional examples is available (27). 

Pyridazinecarboxamides are prepared from the corresponding esters or acid chlorides with ammonia or amines or by partial hydrolysis of cyanopyridazines. Pyridazinecarboxamides with a variety of substituents are easily dehydrated to nitriles with phosphorus oxychloride and are converted into the corresponding acids by acid or alkaline hydrolysis. They undergo Hofmann degradation to give the corresponding amines, while in the case of two ortho carboxamide groups pyrimidopyridazines are formed. 

Other derivatives can be prepared by reaction of the alcohol with an acid anhydride. For example, phthalic or 3-nitrophthalic anhydride (I mol) and the alcohol (Imol) are refluxed for half to one hour in a non-hydroxylic solvent, e.g. toluene or alcohol-free chloroform, and then cooled. The phthalate ester crystallises out, is precipitated by the addition of low boiling petroleum ether or is isolated by ev toration of the solvent. It is recrystallised from water, 50% aqueous ethanol, toluene or low boiling petroleum ether. Such an ester has a characteristic melting point and the alcohol can be recovered by acid or alkaline hydrolysis. 

Note Perhaps because so many halogenoquinoxalines are themselves derived from quinoxahnones, the reverse process of hydrolysis is seldom reported the examples are all special cases in which a passenger group would complicate or preclude a straightforward acidic or alkaline hydrolysis. 

Note Such deacylations have been done by acidic or alkaline hydrolysis to give primary or secondary aminoquinoxalines, both nuclear and extranuclear. Treatment with hydrazine should also achieve deacylation, but there appear to be no recent examples. 

Simple amides are satisfactory protecting groups only if the rest of the molecule can resist the vigorous acidic or alkaline hydrolysis necessary for removal. For this... 

On acid or alkaline hydrolysis, the dihydrooxazines 410 give V-acyl derivatives 411 [74CCC1447 82ZOR181 85ACH(118)139 93T3907]. Under... 

Simple amides are satisfactory protective groups only if the rest of the molecule can resist the vigorous acidic or alkaline hydrolysis necessary for their removal. For this reason, only amides that can be removed under mild conditions have been found useful as amino-protecting groups. Phthalimides are used to protect primary amino groups. The phthalimides can be cleaved by treatment with hydrazine. This reaction proceeds by initial nucleophilic addition at an imide carbonyl, followed by an intramolecular acyl transfer. 

Either acid or alkaline hydrolysis can be applied, converting nicotinamide to nicotinic acid. Alkaline hydrolysis releases also the unavailable vitamers providing the estimation of the total niacin content. Acid hydrolysis, instead, is slower than alkaline hydrolysis therefore the former is usually coupled with enzymatic digestion by using takadiastase, papain, and clarase. Extraction with water and dilute sulfuric or hydrochloride acid has been applied to release the vitamers from the matrix without degrading nicotinamide [598]. 

Thioacetamide decomposition at intermediate pH values, particularly in weakly acidic solutions (pH > 2), has been suggested to occur through a thioacetamide complex rather than through intermediate formation of sulphide [4]. Of course, this process may also occur in parallel with either acid or alkaline hydrolysis of thioacetamide to (ultimately) sulphide at certain pH ranges. It is also possible that this complex-decomposition reaction occurs at both high and low pH values in certain cases. 

Application of gas chromatographic techniques is restricted by the necessary volatility that the analyzed compounds should exhibit. A derivatization reagent is added, in a prior step, to render volatile the components of the analyzed organic materials. In some cases, a prior step consisting of an acid or alkaline hydrolysis of the organic material is necessary for releasing the molecular constituents of the polymeric structure. Inclusion of a prior step in the preparation procedure devoted to the suppression of interfering species is sometimes included. 

Nucleophilic reagents can also react with 2- and 4-aminopyridines at the carbon atom which carries the amino group in a replacement reaction (e.g. 738 — 739) similar to, but far less facile than, that undergone by chloro and alkoxy compounds, etc. In this way aminopyrimidines can be converted into pyrimidinones by direct acidic or alkaline hydrolysis under rather vigorous conditions. 

Due to the relative stability of the niacin vitamers, either acid or alkaline hydrolysis can be used to convert nicotinamide to nicotinic acid for quantitation of both vitamers as nicotinic acid (9,44). Acid hydrolysis is used to quantitate biologically available niacin. Alkaline hydrolysis releases both the biologically available and the unavailable vitamers and provides an estimate of the total niacin content. Because alkaline hydrolysis is much faster than acid hydrolysis, the latter is usually supplemented with enzymatic hydrolysis. The most common enzymes are takadiastase, papain, and clarase. On occasion, organic solvents such as methanol have been used to extract free nicotinic acid. 

Deprotection may be effected by vigorous acidic or alkaline hydrolysis (p. 918). Alternative methods of deprotection are sodium hydride in refluxing dimethoxyethane,227 or by heating with 85 per cent hydrazine hydrate (hydra-zinolysis).228... 

Copolymer. The appearence and properties of a particular copolymer obtained depended to a large degree on the type of monomer with which the copolymer was prepared. LS-(methyl acrylate) and LS-(methyl methacrylate) copolymers were brownish amorphous solids. The former was rubbery and moderately hard and the latter was plastic like and harder than the former. At room temperature, both were insoluble in ordinary solvents and quickly swelled in water to about six times in volume. At elevated temperature, the lignin backbone of these two copolymers could be degraded through acid or alkaline hydrolysis. 

Note The choice between acidic or alkaline hydrolysis may depend on the other substituents present in the molecule. 

Hydrolysis of Protein. The radioactive, proteinaceous residues from the sulfate-injected insects were separated into equal fractions, one of which was hydrolyzed with acid and the other with proteolytic enzyme. Analyses of unlabeled protein were made after acid or alkaline hydrolysis. 

Methyl Ester-Based Processes. The fatty methyl esters are produced predominantly by the transesterification of fats and oils with methanol in the presence of an alkaline catalyst under very mild reaction conditions.l5a,b They are used in the production of lauric-type (Cl2) alcohols. The short-chain fatty methyl esters (C8-Cl0), produced as by-products via the fractional distillation of crude lauric-type (coconut, palm kernel) methyl esters, are converted to fatty acids via acidic or alkaline hydrolysis (Fig. 36.12). The hydrolysis of short-chain fatty methyl esters by stream splitting or Twitchell-type processes is not very efficient because of unfavorable equilibrium constants.16a,b... 

The variations concern pH, temperature, time of processing, and, in the last case additionally, possible ultrasonic treatment. The following step consists in a liquid-phase or solid-phase extraction (SPE). However, other extraction methods like SFE ° also have been used prior to the detection procedure. The final choice of the workup procedure is mainly dependent on the chemical stability of the analyte e.g., benzodiazepines are highly unstable under alkaline conditions, but they are also affected under acid conditions. Alkaline hydrolysis should be avoided for cocaine - however, morphine can be extracted after acid or alkaline hydrolysis. ... 

The GC/MS procedures for methamphetamine are described in Table 4. The papers published in Japanese - have corresponding reports in English. - - Methamphetamine was detected and determined by mass fragmentography in rat hair after administration of the substance. Nine methods also detected the metabolite amphetamine or amphetamine alone. Suzuki et al. determined methamphetamine also in nail, sweat and saliva. The workup (EX after acid or alkaline hydrolysis) and derivatization technique (methanol-trifluoroacetic acid [TEA]) is rather uniform in most procedures. Nakahara et al. ° used methoxyphenamine excretion into beard hair to discuss several washing procedures. Alkaline or methanolic extraction are used with one exception. Derivatization is mainly made by fluorinated anhydrides. A review ° gives details on analytical procedures, incorporation rates of amphetamines from blood to hair, and relationship between drug history and drug distribution in hair. 

Thermal decarboxylation of l-methyl-2-oxo-l,2-dihydro-l,4,5-tri-azanaphthalene-3-carboxylic acid is accompanied by the formation of a red compound as a by-product, to which the dimeric structure 180b has been assigned.261 Acid or alkaline hydrolysis of the ethyl ester of the monomer yields the same dimer. 

Acetylamino-TO-tolylarsinic acid yields this acid when oxidised with aqueous permanganate. The product decomposes at about 230° C., and by acid or alkaline hydrolysis gives 4i-amino-5-carbo(ieyphenylarsinic acid, decomposing at about 245° C. 

Acid or alkaline hydrolysis preferentially breaks the 5 -bond, which is in contrast to the action of phosphodiesterase which attacks only the 3 -bond. 

Many arylsuifonamidopyrazines have been prepared, most usually by the reaction of the (p-acetamido)aryisulfonyl chloride, and aminopyrazine in pyridine (the 7V-acetyl group may be removed by acid or alkaline hydrolysis). In this way the following have been synthesized 2-(A( -acetylsulfanilamido)pyrazine (29) (400, 1175, 1204, 1205) [hydrolyzed by acid (400,1204)and alkali (1205) to 2-sulfanil-amidopyrazine], and various C-alkyl (and C-phenyi) derivatives (420, 535) 2-(p-... 

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