Hydrolysis susceptibility

The hydrolysis susceptibility of a polyester or a polyester-based PU depends on the concentration of ester bonds, on the polyester polyol acidity, on the hydrophobicity of the glycol or dicarboxylic acid used for polyester synthesis, and on the steric hindrance around the ester groups. Low concentration of the ester bonds, low polyester acidity, high comonomer hydrophobicity and high steric hindrance around the ester groups confer hydrolysis resistance to the polyester-based PU. 

Alterations to the fibers that affect the apparent frequency of acidic or basic groups, such as hydrolysis, susceptibility to hydrolysis, or the introduction of sulfonic acid groups [24, 66], can affect the acid- and/or basecombining capacity of hair. Therefore, permanent-waving and especially bleaching can affect these titration parameters [8]. The effects of cosmetic treatments and environment on these parameters are described in detail in Chapter 5. 

The most hydrolysis-susceptible side-substituent is chlorine and hence if preparing polymers from a poly(dichloro)phosphazene precursor, knowledge of the residual chlorines is required [27, 30]. Not only is the P-Cl moiety itself extremely labile, its hydrolysis leads directly to the degradation intermediate hydroxyphosphazene [31] and also produces HCl as a by-product, which is known to further catalyse hydrolysis (see Section 1.1). Although through the partial substitution of poly(dichloro)phosphazene it is thus possible to prepare degradable materials, in practice however, full substitution is usually strived for, not least for the sake of reproducibility. 

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). 

This difference m reactivity especially toward hydrolysis has an important result We 11 see m Chapter 27 that the structure and function of proteins are critical to life Itself The bonds mainly responsible for the structure of proteins are amide bonds which are about 100 times more stable to hydrolysis than ester bonds These amide bonds are stable enough to maintain the structural integrity of proteins m an aqueous environment but susceptible enough to hydrolysis to be broken when the occasion demands... 

Converting the C 2 alkylated derivative to the corresponding malonic acid deriva tive by ester hydrolysis gives a compound susceptible to thermal decarboxylation Tern peratures of approximately 180°C are normally required... 

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. 

Phosphoms oxyfluoride is a colorless gas which is susceptible to hydrolysis. It can be formed by the reaction of PF with water, and it can undergo further hydrolysis to form a mixture of fluorophosphoric acids. It reacts with HF to form PF. It can be prepared by fluorination of phosphoms oxytrichloride using HF, AsF, or SbF. It can also be prepared by the reaction of calcium phosphate and ammonium fluoride (40), by the oxidization of PF with NO2CI (41) and NOCl (42) in the presence of ozone (43) by the thermal decomposition of strontium fluorophosphate hydrate (44) by thermal decomposition of CaPO F 2H20 (45) and reaction of SiF and P2O5 (46). 

Ha.logena.tlon, 3-Chloroindole can be obtained by chlorination with either hypochlorite ion or with sulfuryl chloride. In the former case the reaction proceeds through a 1-chloroindole intermediate (13). 3-Chloroindole [16863-96-0] is quite unstable to acidic aqueous solution, in which it is hydroly2ed to oxindole. 3-Bromoindole [1484-27-1] has been obtained from indole using pytidinium tribromide as the source of electrophilic bromine. Indole reacts with iodine to give 3-iodoindole [26340-47-6]. Both the 3-bromo and 3-iodo compounds are susceptible to hydrolysis in acid but are relatively stable in base. 

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. 

Many tracer chemicals are inherently unstable even as the unlabeled forms. Susceptibility of a chemical to hydrolysis, oxidation, photolysis, and microbiological degradation needs to be evaluated when designing suitable storage conditions for the labeled compound. Eactors that reduce radiolytic degradation, such as dispersal in solution, are apt to increase chemical degradation or instability. 

Carboxyhc acid ester, carbamate, organophosphate, and urea hydrolysis are important acid/base-catalyzed reactions. Typically, pesticides that are susceptible to chemical hydrolysis are also susceptible to biological hydrolysis the products of chemical vs biological hydrolysis are generally identical (see eqs. 8, 11, 13, and 14). Consequentiy, the two types of reactions can only be distinguished based on sterile controls or kinetic studies. As a general rule, carboxyhc acid esters, carbamates, and organophosphates are more susceptible to alkaline hydrolysis (24), whereas sulfonylureas are more susceptible to acid hydrolysis (25). 

At room temperature, ca 60 wt % ethylene oxide is needed to solubilize the fatty acids. Surface activity of the ethoxylates is moderate and less than that of alcohol or alkylphenol ethoxylates (84). The ethoxylates are low foamers, a useful property in certain appHcations. Emulsification is the most important function. Its importance is reflected in the wide range of lipophilic solubiHties available in the commercial products. Like all organic esters, fatty acid ethoxylates are susceptible to acid and alkaline hydrolysis. 

Diorganotin esters of strong acids are relatively stable to hydrolysis under neutral conditions, but generally, diorganotin compounds ate more reactive chemically than the triorganotins. Diorganotin esters of weak acids are somewhat susceptible to hydrolysis, even under neutral conditions, but this reactivity is moderated somewhat by their hydrophobicity. 

Bismuth Salts. Bismuth trioxide dissolves in concentrated solutions of strong oxyacids to yield bismuth salts. In more dilute solutions of strong acids or in solutions of weak acids, the oxide reacts to form bismuthyl or basic salts. The normal salts are very susceptible to hydrolysis. 

Procedures for shipping boric acid esters depend on the particular compound. Aryl borates produce phenols when in contact with water and are therefore subject to shipping regulations governing such materials and must carry a Corrosive Chemical label. Lower alkyl borates are flammable, flash points of methyl, ethyl, and butyl borates are 0, 32, and 94°C, respectively, and must be stored in approved areas. Other compounds are not hazardous, and may be shipped or stored in any convenient manner. Because borate esters are susceptible to hydrolysis, the more sensitive compounds should be stored and transferred in an inert atmosphere, such as nitrogen. 

The toxicity of a few boric acid esters has been summarized (30). In general the toxicities are directiy related to the toxicity of the alcohol or phenol produced on hydrolysis. Methyl borate has an oral rat LD q of 6.14 mL/kg in a range finding test (31) and the percutaneous LD q for the rabbit of 1.98 mL/kg. In eadier work (32), the oral LD q for the rat was 2.82 mL/kg the intraperitoneal LD q was 3.2 mL/kg. It has been shown that the mouse is more susceptible to these compounds than the rat. Methyl borate was found to be moderately irritating in an ocular toxicity test using rabbits (31,32) but only mildly irritating to skin (31). 

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