Hydrolysis attack

The auto-hydrolytic effect of boiling an aqueous solution was also investigated by following changes in the sedimentation and diffusion constants and the intrinsic viscosity. Although the measurements were complicated by the fact that the insoluble portion dissolved as boiling proceeded, the results indicated that the gum molecules were long chains with small adjacent side chains, and that hydrolysis attacked the weaker side chains. 

Nitrenes, like carbenes, are immensely reactive and electrophilic, and the same Wolff-style migration takes place to give an isocyanate. The substituent R migrates from carbon to the electron-deficient nitrogen atom of the nitrene. Isocyanates are unstable to hydrolysis attack by water on the carbonyl group gives a carbamic acid which decomposes to an amine. 

Optimal pH Temperature stability (°C) Source of hemicellulo.se Products of hydrolysis Attack on sugar-beet L-arabinan" Products of attack6 on ... 

A controlled opening of a,(3-epoxy ketones involves reaction with Ph(Me)2SiLi and mild hydrolysis. Attack of the silyllithium reagent on the ketone groups is followed by a Brook rearrangement and p-elimination. " ... 

Because a high proportion of fabric dust collectors are not faced with such thermal or chemical constraints, the most commonly used fibre in dust collection is of polyester origin, this being capable of continuous operation at a reasonably high temperature (150°C) and also competitively priced. On the debit side, polyester is acutely sensitive to hydrolysis attack and if this poses a serious problem, fibres from the acrylic group would be the preferred choice. 

The explanation commonly accepted is that the alkali liberated by hydrolysis attacks any greasy matter on the surface to be cleansed, and, as the fat is dissolved, the particles of dirt are loosened and easily washed off. Berzelius held this view, and considered that the value of a soap depended upon the ease with which it yielded free alkali on solution in water. 

Polypropylene glycol polyol represents a typical polyether polyol. With the ether linkage, the polyurethanes made from this are generally more flexible at lower temperatures. Also, polyurethanes based on this type of polyol backbone are more resistant to hydrolysis attack by water (especially in alkaline solution) than polyurethanes with backbones of polyester. 

Factors other tlian tire Si/Al ratio are also important. The alkali-fonn of zeolites, for instance, is per se not susceptible to hydrolysis of tire Al-0 bond by steam or acid attack. The concurrent ion exchange for protons, however, creates Bronsted acid sites whose AlO tetraliedron can be hydrolysed (e.g. leading to complete dissolution of NaA zeolite in acidic aqueous solutions). 

Acetals are usually liquid they are almost unaffected by alkalis and are not attacked by metallic sodium nor by Fehling s solution. They are identified by reference to the alcohol and aldehyde (or ketone if a ketal) which they yield when hydrolysed in acid solution. Hydrolysis proceeds readily in dilute acid solution e.g., with 3-5 per cent, acid). ... 

The oxidation of the cyclic enol ether 93 in MeOH affords the methyl ester 95 by hydrolysis of the ketene acetal 94 formed initially by regioselective attack of the methoxy group at the anomeric carbon, rather than the a-alkoxy ketone[35]. Similarly, the double bond of the furan part in khellin (96) is converted ino the ester 98 via the ketene acetal 97[l23],... 

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

Because the positive charge m an allylic carbocation is shared by two carbons there are two potential sites for attack by a nucleophile Thus hydrolysis of 3 chloro 3 methyl 1 butene gives a mixture of two allylic alcohols... 

The mechanisms of all the reactions cited m Table 20 1 are similar to the mecha nism of hydrolysis of an acyl chlonde outlined m Figure 20 2 They differ with respect to the nucleophile that attacks the carbonyl group... 

Once It was established that hydroxide ion attacks the carbonyl group in basic ester hydrolysis the next question to be addressed concerned whether the reaction is concerted or involves a tetrahedral intermediate In a concerted reaction the bond to the leaving group breaks at the same time that hydroxide ion attacks the carbonyl... 

FIGURE 27 19 Proposed mechanism of hydrolysis of a peptide catalyzed by carboxypeptidase A The peptide is bound at the active site by an ionic bond between its C terminal ammo acid and the positively charged side chain of arginine 145 Coordination of Zn to oxygen makes the carbon of the carbonyl group more positive and increases the rate of nucleophilic attack by water... 

Dry chlorine has a great affinity for absorbing moisture, and wet chlorine is extremely corrosive, attacking most common materials except HasteUoy C, titanium, and tantalum. These metals are protected from attack by the acids formed by chlorine hydrolysis because of surface oxide films on the metal. Tantalum is the preferred constmction material for service with wet and dry chlorine. Wet chlorine gas is handled under pressure using fiberglass-reinforced plastics. Rubber-lined steel is suitable for wet chlorine gas handling up to 100°C. At low pressures and low temperatures PVC, chlorinated PVC, and reinforced polyester resins are also used. Polytetrafluoroethylene (PTFE), poly(vinyhdene fluoride) (PVDE), and... 

Fatty acids are susceptible to oxidative attack and cleavage of the fatty acid chain. As oxidation proceeds, the shorter-chain fatty acids break off and produce progressively higher levels of malodorous material. This condition is known as rancidity. Another source of rancidity in fatty foods is the enzymatic hydrolysis of the fatty acid from the glycerol. The effect of this reaction on nutritional aspects of foods is poorly understood andhttie research has been done in the area. 

Hydantoins can react with electrophiles at both nitrogen atoms and at C-5. The electrophilic carbonyl groups can be attacked by nucleophiles, leading to hydrolysis of the ring or to partial or total reduction of the carbonyl system. Other reactions are possible, including photochemical cleavage of the ring. 

Although reasonably stable at room temperature under neutral conditions, tri- and tetrametaphosphate ions readily hydrolyze in strongly acidic or basic solution via polyphosphate intermediates. The hydrolysis is first-order under constant pH. Small cycHc phosphates, in particular trimetaphosphate, undergo hydrolysis via nucleophilic attack by hydroxide ion to yield tripolyphosphate. The ring strain also makes these stmctures susceptible to nucleophilic ring opening by other nucleophiles. 

Properties ndReactions. Phosphoms pentachloride, PCl, is a pale, greenish yellow soHd having a pungent odor (see Table 7). It is made from PCl and chlorine. Water attacks PCl and the violent hydrolysis proceeds in two stages. 

Emissions During Exterior End Use. When flexible PVC is used in exterior appHcations plasticizer loss may occur due to a number of processes which include evaporation, microbial attack, hydrolysis, degradation, exudation, and extraction. It is not possible, due to this wide variety of contribution processes, to assess theoretically the rate of plasticizer loss by exposure outdoors. It is necessary, therefore, to carry out actual measurements over extended periods in real life situations. Litde suitable data have been pubHshed with the exception of some studies on roofing sheet (47). The data from roofing sheet has been used to estimate the plasticizer losses from all outdoor appHcations. This estimate may weU be too high because of the extrapolation involved. Much of this extracted plasticizer does not end up in the environment because considerable degradation takes place during the extraction process. 

It is generally accepted that transamidation is not a concerted reaction, but occurs through the attack of a free end on the amide group via aminolysis (eg, eq. 4) or acidolysis (eg, eq. 3) (65). Besides those ends always present, new ends are formed by degradation processes, especially hydrolysis (eq. 5), through which the amide groups are in dynamic equiUbrium with the acid and amine ends. 

Noryl is a rigid dimensionally stable material. Dimensional stabiUty results from a combination of low mold shrinkage, low coefficient of thermal expansion (5.9 x 10 per° C), good creep resistance (0.6—0.8% in 300 h at 13.8 MPa (2000 psi)), and the lowest water absorption rate of any of the engineering thermoplastics (0.07% in 24 h at room temperature). Noryl resins are completely stable to hydrolysis. They are not affected by aqueous acids or bases and have good resistance to some organic solvents, but they are attacked by aromatic or chlorinated aUphatic compounds. 

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