Acid, hydrolysis

In considering the acid hydrolysis of esters, we should remember that esters are weak bases. Most of them show a molar freezing point depression of two when they are dissolved in 100 per cent sulfuric acid. Presumably the two species arise from the reaction (see p. 36)  

There might seem to be some confusion as to the oxygen atom with which the proton is associated. From, our discussion of polarizability (p. 28) and the reactivity of carbonyl groups (p. 156), we should expect the proton to be found on the keto-oxygen atom  

In discussing esterification and hydrolysis, however, most authors prefer to show the proton on the ethereal oxygen atom and to consider this form 

1 For an excellent review from which much of this material was adapted, see Day and Ingold, Trans. Faraday 80c., 37, 686 (1941). 

Actually, these two views are not incompatible. Although addition probably occurs predominately at the keto-oxygen atom, nevertheless it seems reasonable to suppose that an equilibrium exists between the two cations  

The N-glycosidic purine-carbohydrate bond in both types of nucleic acid is particularly susceptible to acids whereas the pyrimidine nucleosides and -nucleotides are quite resistant. Acid removes the phosphoric acid moiety much more easily from purine nucleotides than from pyrimidine nucleotides. 

Cleavage o Purines and Pyrimidines from Deoxyribonucleic Acids according to Yischer and Chargaff and to Wyatt [99,105] 

Procedure 0.5 ml 98% formic acid is added to 10— 20 mg of deoxyribonucleic acid which has been dried in vacuo at 40—60° C and the mixture heated for 30 min at 175° C in a thick-walled, sealed glass tube, placed in an electric oven. After cooling, the tube is carefully opened and the formic acid removed in a desiccator over potassium hydroxide. The residue is taken up in 3—4 ml N hydrochloric acid and the solution used for analysis of the purine and pyrimidine bases. 

Ribonucleic acids are not completely hydrolysed under these conditions. 

Cleavage of Purines and Pyrimidines from Ribo- and Deoxyribonucleic Acids according to Marshak and Vogel [46,105] 

The preceding techniques are applicable only for the measurement of the rate of hydrolysis of peptides and proteins, and the methods employed in the sequence analysis of polypeptides are required for identification of the residues which form the susceptible bonds. These methods have been reviewed in detail elsewhere (Moore and Stein, 1956 Anfinsen and Redfield, 1956 Greenstein and Winitz, 1961 Canfield and Anfinsen, 1963) and do not require comment here. 

Partial Acid Hydrolysis of Proteins The Specificity of Acid Hydrolysis 

Several workers subsequently confirmed these observations. Stein et al. (1944) examined the hydrolytic products with the manometric methods developed by Van Slyke and co-workers (1941) and demonstrated that dipeptides represented the overwhelming proportion of the products formed when silk fibroin was hydrolyzed for 96 hr at 40°C in concentrated HCl. After 40 hr, the hydrolyzate contained about 25% free amino acids with the remainder of the residues existing as di- and tripeptides. Bull and Hahn (1948), using a spread monolayer technique for estimating molecular weights, examined partial acid hydrolysis of egg albumin. By this method, immediate cleavage of about fifty bonds was observed when egg albumin was dissolved in 7.6 N HCl at 60°C. The remainder of the bonds were hydrolyzed at much slower rates. 

These results show that the course of partial acid hydrolysis is not a random process but that it exhibits a certain degree of specificity. For purposes of discussion it is convenient to consider separately each aspect of this specificity. 

The influence of electrostatic effects on the rate of hydrolysis of peptides is demonstrated vividly by the studies of Long and co-workers (1963) who made quantitative kinetic studies of the parallel and consecutive reactions which occur on hydrolysis of tripeptides. These workers employed an 

Barley starches exhibit a relatively high rate of acid hydrolysis during the first 10 days, followed by a slower rate thereafter.28,39 The extent of degradation follows the order waxy normal high-amylose (Table 16.6). This order is similar to that 

For amino sugar sulfates, the position is complicated by the possibility of JV-sulfate (sulfoamino) being present. The iV-sulfate link is, however, much more labile to acids than the 0-sulfate link, and they can be readily distinguished in this way.  

Because of uncertainties in the present methods for tryptophan analysis, it is obvious that a satisfactory general procedure remains to be found 135, 353). Acid hydrolysis with /7-toluenesulfonic 233, 234) or mercaptoethanesulfonic acid 299) seems to be the most reliable known method, even though the analytical figures for tryptophan have to be checked by different methods. 

In this section, methods for the quantitative determination of tryptophan, free or bound in a polypeptide chain, are discussed in more detail. 

The lability of tryptophan under the conditions usually employed for acid hydrolysis of proteins (6N HCl, 24 hrs, in sealed tubes under vacuum) is not due to instability of the indole nucleus under such conditions, but to side reactions involving non-proteinaceus material, like carbohydrates, or to the presence of particular amino acids in the acidic hydrolysis mixture. In fact, gramicidin A, a pentadecapeptide containing, apart from tryptophan, only purely aliphatic amino acids like glycine, alanine, leucine and valine, gives a quantitative recovery of tryptophan after acid hydrolysis in 6N HCl (l20). 

Mondino and Bongiovanni 262) observed that cystine, tryptophan and to a lesser extent threonine and serine were degraded when a mixture of all the common amino acids found in proteins was hydrolyzed in 6N HCl by an open-flask technique and analyzed on an automatic amino acid analyzer. More recently, Gruen 157) carefully studied the separate effect of each of the other commonly occuring amino acids on the recovery of tryptophan, using the standard procedure for amino acid analysis, whereby tryptophan is eluted from the short column along with the basic amino acids as a well resolved peak appearing before lysine 135, 369). 

Gruen (757) found that the presence of most of the amino acids tested during hydrolysis does not affect the tryptophan recovery. Of the hydroxyamino acids, threonine had no effect at all, while tyrosine has a small effect. On the other hand serine was found to reduce the recovery of tryptophan by about 10% due to a deamination reaction of serine. This produces pyruvic acid which, as a ketoacid, interacts with the indole nucleus of tryptophan (287). Whereas cysteine had no effect, cystine caused a substantial loss of tryptophan (about 40%), and was itself recovered on the analyzer partly in the reduced cysteine form. These results would indicate that a major factor in the loss of tryptophan during acid hydrolysis of a protein is degradative oxidation by cystine. 

Continental water contains dissolved species that render it acidic. The acidity comes from a variety of sources from the dissociation of atmospheric C02 in rainwater—and particularly from dissociation of soil-zone C02 (Section 4.4.2)— to form H2C(and natural and anthropogenic sulphur dioxide (S02) to form H2S03 and H2S04 (see Boxes 3.7 3.8). Reaction between a mineral and acidic weathering agents is usually called acid hydrolysis. The weathering of CaCO, demonstrates the chemical principle involved  

Acid hydrolysis of a simple silicate, for example the magnesium-rich olivine, forsterite, is summarized by  

Note that the dissociation of H2C03 forms the ionized HC03, which is a slightly stronger acid than the neutral molecule (ITSiCD released by the destruction of the silicate. 

The combined effects of dissolving C02 into soilwater (eqn. 4.7), the subsequent dissociation of H2C03 (eqn. 4.8) and the production of HCO) by acid hydrolysis weathering reactions (eqns. 4.11 4.12) mean that surface waters have near-neutral pH, with HC03 as the major anion. 

Sousa et al. [46] studied the mechanical properties of polypropylene (PP) composites reinforced with pretreated pineapple fibers with sulfuric solution. Pineapple fibers were extracted from residue SuFresh and dried at 80°C for 24 h. After being ground in a mill and sieved, the fibers were pretreated in a 350 L stainless steel reactor, under these conditions 1.0% (w/v) H SO solution in a 1 10 solid liquid ratio, 120°C for 10 min. 

Samples Tensile Strength (MPa) Tensile Modulus (MPa) Flexural Strength (MPa) Flexural Modulus (MPa) Impact Strength (J.m- ) 

Because of this fact, results obtained in the impact test showed composites have more strength when compared to pure polypropylene. This increase occurred due to 

The pineapple fibers from the juice residue reinforced with polypropylene composites presented higher strength compared to modified fibers from the juice residue reinforced with polypropylene composites. 

The amount of reinforcement in the matrix also contributes to the increase in strength. The modification of the pineapple fibers from the juice residue improved the adhesion between fiber/matrix, facilitating the energy transfer of impact, which is one of the influencing factors of this property. However, the unmodified fibers also facilitated the adhesion this occurred because the acidity in the juice production favored treatment in the fibers from the residue. 

138 I Z Preparation, Properties and Chemitxil Modification of Nanosized Cellulose Fibrils 

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Ci-,H2,N04. Colourless prisms, m.p. 98°C. Obtained from coca, either by direct purification, or by acid hydrolysis of the mixed alkaloids to ecgonine, which is then methylated and benzoylated. Coca consists of the dried leaves of Eryihroxyluni coca and Erythroxylum iruxillense, shrubs growing in Bolivia and Peru. 

C7H6O5. Colourless crystals with one molecule of water, m.p. 253" C, sparingly soluble in water and alcohol. It occurs free in woody tissue, in gall-nuts and in tea, and is a constituent of the tannins, from which it can be obtained by fermentation or by acid hydrolysis. It gives a blue-black colour with Fe and is used in the manufacture 6f inks. On heating it gives pyrogallol. 

Acidic Hydrolysis. Hot concentrated caustic alkalis first hydrolyse off the ethyl group, and then split the molecule to give one equivalent of acetic acid and one equivalent of the mono- or di-substituted acetic acid (as their alkali salts). 

For practice, the student should carry out both alkaUne (compare Section 111,83) and acid hydrolysis of acetonitrile, n-valeronitrile (n-butyl cyanide) and n-capronitrile (n-amyl cyanide). 

With concentrated alkali, fission occurs at the position adjacent to the carbonyl group to give acetic acid and a mono-substituted acetic acid the process is termed acid hydrolysis. 

Benzanilide and similar compounds are very slowly hydrolysed by concentrated hydrochloric acid hydrolysis is quite rapid with 60-70 per cent, sulphuric acid (for experimental details, see Section IV,52). In the preliminary experiment boil 0 5-1 Og. of the compound with 10-20 ml. of dilute sulphuric acid (1 1 by volume) imder reflux for 20-30 minutes. Dilute with 10ml.of water and filteroflfanyacid which may be precipitated if the carboxyhc acid is hquid and volatile, distil it directly from the reaction mixture. Render the residue alkaline and isolate the base as above. 

In the above reaction one molecular proportion of sodium ethoxide is employed this is Michael s original method for conducting the reaction, which is reversible and particularly so under these conditions, and in certain circumstances may lead to apparently abnormal results. With smaller amounts of sodium alkoxide (1/5 mol or so the so-called catal3rtic method) or in the presence of secondary amines, the equilibrium is usually more on the side of the adduct, and good yields of adducts are frequently obtained. An example of the Michael addition of the latter type is to be found in the formation of ethyl propane-1 1 3 3 tetracarboxylate (II) from formaldehyde and ethyl malonate in the presence of diethylamine. Ethyl methylene-malonate (I) is formed intermediately by the simple Knoevenagel reaction and this Is followed by the Michael addition. Acid hydrolysis of (II) gives glutaric acid (III). 

Complete hydrolysis may be efiected by boiling either with 10 per cent, sodium hydroxide solution or with 10 per cent, sulphuric acid for 1-3 hours. It is preferable to employ the non-volatile sulphuric acid for acid hydrolysis this... 

TBS can be selectively removed in the presence of TBDPS by acid hydrolysis. 

The exocyclic 1,3-dioxolane ring is much more vulnerable to acid hydrolysis than the ring connected with the acetal group. Partial deprotection of the side-chain is easily achieved by treatment with sulfurie acid. 

J lie decarboxylation is frequently the most troublesome step in this sequence. Attempts at simple thermal decarboxylation frequently lead to recycliz-ation to the lactam. The original investigators carried out decarboxylation by acidic hydrolysis and noted that rings with ER substituents were most easily decarboxylated[2]. It appears that ring protonation is involved in the decarboxylation under hydrolytic conditions. Quinoline-copper decarboxylation has been used successfully after protecting the exocyclic nitrogen with a phthaloyl, acetyl or benzoyl group[3]. 

Acidic hydrolysis of 2,5-dipheny]-4-aminothiazole similarly gives product 233, resulting from nucleophilic attack on C-4 (Scheme 142) (465). 

Acidic hydrolysis of these compounds regenerates the initial 2-aminothiazole (510). The reduction of 2-thiazolylamidines provides a good synthetic route to secondary 2-aminothiazoles (see Section I.l.E). They can be used as starting materials to obtain biheterocyclic products such as l-(5-nitro-2-thiazolyl)-2-thioxoimidazolidine (275) (Scheme 169) (511). 

Benzylidenehydrazinoselenazoies are stable to acids and do not decompose with time. The isopropylidene homologs are only stable in the form of the hydrochloride, and they can undergo acid hydrolysis, thus providing a convenient pathway to the free hydrazine (32). Hydrolysis is carried out w ith hot 2 N hydrochloric acid, which, after recooling and filtration, leads to 2-hydrazinoselenazole hydrochloride, yielding the free base upon neutralization (Scheme 19, Table X-6). 

The Claisen condensation of an aliphatic ester and a thiazolic ester gives after acidic hydrolysis a thiazolylketone (56). For example, the Claisen condensation of ethyl 4-methyl-5-thiazolecarboxylate with ethyl acetate followed by acid hydrolysis gives methyl 4-methyl-5-thiazolyl ketone in 16% yield. 

The nucleophiles used are OH (32) [the 2-hydroxythiazole can also be obtained by acidic hydrolysis with strong mineral acids (33)], OR" (5, 8, 30, 34), SR" (8, 9, 12), ArSH (35), and amines (4, 7, 14, 33). Benzamide also reacts with 2-bromothiazole, yielding 2-benzamidothiazole (36). Sulfonamide also reacts with 2-halogenothiazoles in presence of a base and copper powder, yielding 2-sulfonamidothiazoles (37, 38). 

In an extension of the work described m the preceding section Bender showed that basic ester hydrolysis was not concerted and like acid hydrolysis took place by way of a tetrahedral intermediate The nature of the experiment was the same and the results were similar to those observed m the acid catalyzed reaction Ethyl benzoate enriched m 0 at the carbonyl oxygen was subjected to hydrolysis m base and samples were isolated before saponification was complete The recovered ethyl benzoate was found to have lost a por tion of Its isotopic label consistent with the formation of a tetrahedral intermediate... 

Nitriles are classified as carboxylic acid derivafives because fhey are convened fo car boxylic acids on hydrolysis The condifions required are similar fo fhose for fhe hydrol ysis of amides namely healing m aqueous acid or base for several hours Like fhe hydrolysis of amides nilrile hydrolysis is irreversible m fhe presence of acids or bases Acid hydrolysis yields ammonium ion and a carboxylic acid... 

L (+) Arabmose is a naturally occurring L sugar It is obtained bj acid hydrolysis of the polysaccharide present in mesquite gum Write a Fischer pro ection for L (+) arabmose... 

D (+) Galactose is a constituent of numerous polysaccharides It is best obtained by acid hydrolysis of lactose (milk sugar) a disaccharide of d glucose and d galactose L (—) Galactose also occurs naturally and can be prepared by hydrolysis of flaxseed gum and agar The principal source of d (+) mannose is hydrolysis of the polysaccharide of the ivory nut a large nut like seed obtained from a South American palm... 

Cyanogemc glycosides are potentially toxic because they liberate hydrogen cyanide on enzyme catalyzed or acidic hydrolysis Give a mechanistic explanation for this behavior for the specific cases of... 

Acid hydrolysis cleaves the amide bonds of the 2 4 dimtrophenyl labeled peptide giving the 2 4 dimtrophenyl labeled N terminal ammo acid and a mixture of unlabeled ammo acids... 

The sequence of each different peptide or protein is important for understanding the activity of peptides and proteins and for enabling their independent synthesis, since the natural ones may be difficult to obtain in small quantities. To obtain the sequence, the numbers of each type of amino acid are determined by breaking down the protein into its individual amino acids using concentrated acid (hydrolysis). For example, hydrolysis of the tetrapeptide shown in Figure 45.3 would give one unit of glycine, two units of alanine, and one unit of phenylalanine. Of course, information as to which amino acid was linked to which others is lost. 

COPPERALLOYS - CAST COPPER ALLOYS] (Vol 7) -for acid hydrolysis containers [SYRUPS] (Vol 23)... 

It was not until the twentieth century that furfural became important commercially. The Quaker Oats Company, in the process of looking for new and better uses for oat hulls found that acid hydrolysis resulted in the formation of furfural, and was able to develop an economical process for isolation and purification. In 1922 Quaker announced the availability of several tons per month. The first large-scale appHcation was as a solvent for the purification of wood rosin. Since then, a number of furfural plants have been built world-wide for the production of furfural and downstream products. Some plants produce as Httie as a few metric tons per year, the larger ones manufacture in excess of 20,000 metric tons. 

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