Hydrolysis basic

Basic hydrolysis of proteins by either Ba(OH)2 or NaOH has been considered preferable to acid hydrolysis for tryptophan analysis unfortunately, the method does not always give satisfactory results. Spies and Chambers (380) studied factors affecting the stability of tryptophan in 5N NaOH. They found that tryptophan is more labile when the amino acid is peptide-linked than in the free form and that losses depend on protein composition. Oelshlegel et ai (281) hydrolyzed proteins with NaOH in the presence of thioglycolic acid, the recoveries of tryptophan being 89-96%. 

The recovery of tryptophan after basic hydrolysis could be improved by storing the sample at pH 4.25 instead of at pH 2.2, since it has been found that tryptophan undergoes a slow destruction in citrate buffer at acid pH values (197). 

Carbohydrate does not interfere in the tryptophan analysis using basic hydrolysis. This allows use of the method in the analysis of samples with appreciable carbohydrate content, including the analysis of tryptophan in foods. 

In basic hydrolysis there is only one positive center at which attack vould be expected to occur. It is the carbonyl carbon atom  

Decomposition of this addition complex could then occur either by the oss of a hydroxide ion (i.e., by a reversal of the step by which it was ormed) or by. the separation of an alkoxide ion  

The formation of amides from esters appears to be a closely related process.17 Here we may suppose that the reaction proceeds similarly through an amide ion  

For the saponification of esters, evidence similar to that on p. 227 indicates that the reaction usually proceeds with acyl-oxygen fission. The most self-contained proof again has been obtained by the use of Ols. The alkaline hydrolysis of amyl acetate in water containing this isotope showed that the amyl alcohol which was formed contained only O16 18 

Saponification is kinetically first order in ester and first order in hydroxide ion. Taken as a whole, then, the reaction may be regarded as a displacement process in which the rate-determining step involves the attack of hydroxide ion and the separation of an alkoxide ion. In agreement with this point of view, the reaction is aided by electron withdrawal from the carbonyl group and hindered by electron release or an increase in the bulk of R.10 

Thus phenolic glycosides are cleaved much more rapidly than are alkyl glycosides. Participation from 2-0- and 6-0-alkoxy groups play an important role. Methyl (3-D-glucopyranoside in 2.5 molar aqueous sodium hydroxide at 170 °C undergoes alkaline cleavage, accompanied by further decomposition.218 

By contrast, phenyl a-D-mannopyranoside under the same conditions gives only methyl a-D-mannopyranoside. It was suggested that neighboring group participation from the 2-oxygen atom produces 1,2-anhydro-D-mannopyranose, which then reacts with methoxide ion to give the methyl mannoside.219 

A somewhat different mechanism involving participation from the 2-oxyanion has been proposed from the observation that p-nitrophenyl a-D-glucopyranoside is cleaved 105 times faster than the corresponding phenyl glucopyranoside in 3.9 molar aqueous KOH at 60 °C, suggesting initial nucleophilic attack by 0-2 on the aryl group. 

The aryl group of the intermediate Meisenheimer complex then migrates to 0-2 and from there to 0-3, after which breakdown to saccharinic acids occurs.220 

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In 1880, R. Andreasch (52) confirmed the new formula (37) by preparing thiohydantoine through condensation of thioglycolic acid with cyanamide (the reverse reaction of the basic hydrolysis of thiohydantoin). 

Ester hydrolysis in base is called saponification, which means soap making Over 2000 years ago the Phoenicians made soap by heating animal fat with wood ashes Animal fat is rich m glycerol triesters and wood ashes are a source of potassium car bonate Basic hydrolysis of the fats produced a mixture of long chain carboxylic acids as their potassium salts... 

In base the tetrahedral intermediate is formed m a manner analogous to that pro posed for ester saponification Steps 1 and 2 m Figure 20 8 show the formation of the tetrahedral intermediate m the basic hydrolysis of amides In step 3 the basic ammo group of the tetrahedral intermediate abstracts a proton from water and m step 4 the derived ammonium ion dissociates Conversion of the carboxylic acid to its corresponding carboxylate anion m step 5 completes the process and renders the overall reaction irreversible... 

We already discussed bolh Ihe acidic and basic hydrolysis of amides (see Seclion 20 17) All lhal remains to complete Ihe mechamslic piclure of nilrile hydrolysis is to examine Ihe conversion of Ihe nilnle to Ihe conespondmg amide... 

Basic hydrolysis of secondary alkyl-substituted siUcon and germanium peroxides results in oxygen—oxygen bond cleavage. 

Acidic hydrolysis of these hydroxyaLkyl hydroperoxides yields carboxyUc acids, whereas basic hydrolysis regenerates the parent aldehyde, hydrogen peroxide, and often other products. When derived from either aldehydes or cycHc ketones, peroxides (1, X = OH, = H, R, = alkylene or... 

Acid hydrolysis of peroxides (4) and (5) generates carbonyl compounds (parent ketones or aldehydes) and hydrogen peroxide. Basic hydrolysis of cycHc diperoxides with a-hydrogen (those from aldehydes) yields carboxyHc acids (44) ... 

Also, basic hydrolysis or pethydtolysis of diacyl peroxides has been used to produce petoxycatboxyhc acids (44,181). Pethydtolysis produces two moles of the petoxycatboxyhc acid salt ... 

Diels-Alder reaction of 2-bromoacrolein and 5-[(ben2yloxy)meth5i]cyclopentadiene in the presence of 5 mol % of the catalyst (35) afforded the adduct (36) in 83—85% yield, 95 5 exo/endo ratio, and greater than 96 4 enantioselectivity. Treatment of the aldehyde (36) with aqueous hydroxylamine, led to oxime formation and bromide solvolysis. Tosylation and elimination to the cyanohydrin followed by basic hydrolysis gave (24). 

Treatment of (89) with lead tetraacetate generates the unstable open-ring aldehyde (90) which is quickly converted to a dimethylacetal (91). Following basic hydrolysis of the methyl ester and acetates, the acetal is cleaved with aqueous acid to produce TxB2. A number of other approaches, including one starting from the Corey aldehyde, have been described (58). 

Complete basic hydrolysis, followed by the quantitative measurement of hydrogen formed, can be used to determine the number of Si—H and Si—Si bonds present in a particular compound. One molecule of H2 is Hberated for each Si—H and Si—Si bond present. The total siUcon content can be obtained from analysis of the resulting siUcate solution. 

The basic hydrolysis of tri alkyl tin haUdes and other salts forms bis(oxide)s since, except for trimethyl tin, hydroxides are unstable towards dehydration at room temperature. With tin aryl, aralkyl, and cycloalkyltin compounds, the hydroxides can be isolated. Although quite stable, they exist in mobile equiUbrium with the bisoxide and water and are easily dehydrated. Trimethyl tin hydroxide is exceptionally stable towards dehydration. 

Hydrolysis reactions involving tetrahedral intermediates are subject to steric and electronic effects. Electron-withdrawing substituents faciUtate, but electron-donating and bulky substituents retard basic hydrolysis. Steric effects in acid-cataly2ed hydrolysis are similar to those in base-cataly2ed hydrolysis, but electronic effects are much less important in acid-cataly2ed reactions. Higher temperatures also accelerate the reaction. 

This order was chosen so that DDQ (dichlorodicyanobenzoquinone) treatment would not oxidize a dep otected allylic alcohol at C.73, and so that the C.47 hemiketal would still be protected (as the ketal) during basic hydrolysis (step 3). 

AC2O, FeCl3, Et20, 76-93% yield.These conditions give the acetate of the alcohol, which can then be cleaved by simple basic hydrolysis. 

The greater bulkiness of the TIPS group makes it more stable than the /-butyldi-methylsilyl (TBDMS) group, but not as stable as the /-butyldiphenylsilyl (TBDPS) group to acidic hydrolysis. The TIPS group is more. stable to basic hydrolysis than... 

The stability of the TPS group to basic hydrolysis is similar to that of the TMS group, but its stability to acid hydrolysis is about 400 times greater than the TMS group. ... 

The following derivatives represent protective groups that contain an auxiliary functionality, which when chemically modified, results in intramolecular, assisted cleavage, thus increasing the rate of cleavage over simple basic hydrolysis. 

Bu4N F , THF, "2 min. The TBDS group is less reactive toward tri-ethylammonium fluoride than is the TIPDS group. It is stable to 2 M HCl, aq. dioxane, oyemight. Treatment with 0.2 MNaOH, aq. dioxane leads to cleavage of only the Si—O bond at the 5 -position of the uridine derivative. The TBDS derivative is 25 times more stable than the TIPDS derivative to basic hydrolysis. 

Cyclic carbonates are veiy stable to acidic hydrolysis (AcOH, HBr, and H2SO4/ MeOH) and are more stable to basic hydrolysis than esters. 

Aiyl benzoates, stable to alkylation conditions using K2C03/Me2S04, are cleaved by more basic hydrolysis (KOH). They are stable to anhydrous hydrogen chloride, but are cleaved by hydrochloric acid ... 

Monoesterification of a symmetrical dihydroxy aromatic compound can be effected by reaction with polymer-bound benzoyl chloride (Pyr, benzene, reflux, 15 h) to give a polymer-bound benzoate, which can be alkylated with diazomethane to form, after basic hydrolysis (0.5 M NaOH, dioxane, H2O, 25°, 20 h, or 60°, 3 h), a monomethyl ether. ... 

Butyl esters are stable to mild basic hydrolysis, hydrazine, and ammonia they are cleaved by moderately acidic hydrolysis. 

The picolyl ester has been prepared from amino acids and picolyl alcohol (DCC / CH2CI2, 20°, 16 h, 60% yield) or picolyl chloride (DMF, 90-100°, 2 h, 50% yield). It is cleaved by reduction (H2/Pd-C, aq.= FtOH, 10 h, 98% yield Na/NH3, 1.5 h, 93% yield) and by basic hydrolysis (1 NaOH, dioxane, 20°, 1 h, 93% yield). The basic site in a picolyl ester allows its ready separation by extraction into an acidic medium. ... 

The first, and still widely used, polymer-supported ester is formed from an amino acid and a chloromethylated copolymer of styrene-divinylbenzene. Originally it was cleaved by basic hydrolysis (2 N NaOH, FtOH, 25°, 1 h). Subsequently, it has been cleaved by hydrogenolysis (H2/Pd-C, DMF, 40°, 60 psi, 24 h, 71% yield), and by HF, which concurrently removes many amine protective groups. Monoesterification of a symmetrical dicarboxylic acid chloride can be effected by reaction with a hydroxymethyl copolymer of styrene-divinylbenzene to give an ester a mono salt of a diacid was converted into a dibenzyl polymer. ... 

Silyl esters are stable to nonaqueous reaction conditions. A trimethylsilyl ester is cleaved by refluxing in alcohol the more substituted and therefore more stable silyl esters are cleaved by mildly acidic or basic hydrolysis. 

These derivatives are prepared to protect a-hydroxy carboxylic acids they are cleaved by acidic hydrolysis of the acetal structure (HCl, DMF, 50°, 7 h, 71% yield), or basic hydrolysis of the lactone. ... 

Thiocarbamates, formed by reaction of a thiol with an isocyanate, are stable in acidic and neutral solutions and are readily cleaved by basic hydrolysis. The... 

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