Acid acceptors, hydrochloric

As in dry compounding, acid acceptors must be incorporated into neoprene latices because of the wide use of these latices in coating fabrics and metals. The hydrochloric acid that forms during service life has a particularly destmetive effect on coated cotton fabrics that are not adequately protected. High zinc oxide concentration (ca 15 parts) and use of 0.4 parts AJ-phenyl-AT(p-toluenesulfonyl)-/)-phenylenediamine (Aranox, Uniroyal) as an antioxidant provides adequate protection. 

The hydrohalide is liable to dehydrochlorination, particularly when moist acid is used in its preparation, so that hydrochloric acid acceptors such as lead carbonate are useful stabilisers. Dibutyl phthalate and tritolyl phosphate are effective plasticisers. Rubber hydrochloride is used as a packaging film (Pliofilm) and as a rubber-to-metal bonding agent (e.g. Typly). 

Acid acceptor. This is the main function of metal oxides in CR adhesive formulations. Upon age, small amounts of hydrochloric acid are released which may cause discolouration and substrate degradation. Magnesium oxide (4 phr) and zinc oxide (5 phr) act synergistically in the stabilization of solvent-borne polychloroprene adhesives against dehydrochlorination. 

This material can be prepared, e.g, by reaction of prednisolone-21-chloroacetate in solvent with the sodium or potassium salt of the corresponding aliphatic or aromatic acid, or by reaction of prednisolone with the chloride of the corresponding acyl-glycolic acid, in the presence of a hydrochloric acid acceptor. 

Ill terms of llie deliinlioii that an arid is a proton donor and a base is a proton acceptor, hydrochloric acid, water, and ammonia (NH3) are adds in the reactions... 

Diacyl chlorides react with glycols or other diols such as bisphenols without catalyst, forming polyesters in the presence of an acid acceptor removal of the hydrochloric acid formed is important to the equilibrium... 

In interfacial polyamidation the reaction takes place close to the interface between a solution or suspension (usually aqueous) of the diamine and a solution of the diacyl or disulphonyl chloride in an immiscible organic solvent. The aqueous layer often contains an acid acceptor such as triethylamine, pyridine, sodium hydroxide or sodium carbonate, to neutralize the hydrochloric acid produced in the reaction. Often an emulsifier is used to increase interfacial area. The reaction is believed to occur just within the organic solvent layer. The rate of reaction is so fast that the process becomes diffusion-controlled. 

As with interfacial polycondensation an acid-acceptor is necessary to neutralize the hydrochloric acid formed in the reaction. These low-temperature poly condensation reactions are irreversible, and the acid-acceptor is necessary only to keep the reacting diamine free for reaction with the acid chloride. iV,iV-Dimethylacetamide and related solvents are often employed. Ar,A-Dimethylformamide cannot be used as it reacts with the acid chloride, and only low-molecular-weight polymer results. These amide solvents form loose complexes with the hydrochloric acid produced during the polymerization, and no additional acid-acceptor is needed. However, the final solutions are usually neutralized to minimize corrosion of metallic equipment during later steps such as spinning, and to provide small amounts of water often found necessary for the long-term stability of the polymer solutions [111]. 

Acid acceptors are used when acids may be involved in the degradation of the polymer. Calcium stearate is often used with polypropylene to neutralize any mineral acids, such as hydrochloric acid, that might result from the reaction of water with catalyst residues. Various mixed metal laurates are used as stabilizers in polyvinyl chloride. Efforts are underway to replace the cadmium in some of these mixtures (see Chap. 4). Epoxidized soybean oil has been used as the acid acceptor, along with dioctyltinbis(thiogly-colate), to improve the heat stability of polyvinyl chloride.27... 

Alternatively, the same polyester can be prepared by reacting polymethylene bis(p-hydroxybenzoates) and polymethylene bis(p-chloroformylbenzoates) in tetrachlo-roethane using pyridine as the hydrochloric acid acceptor, according to the reaction scheme illustrated in Fig. 5. 

For the preparation of the aminoesters [9]-[10] and the aminoalcohols (12-amino- octadecanol [17] and 9-aminooctadecanol [18], the keto esters [13],[19] or keto [20]-[21] were reacted with hydroxylamine. Two different reaction sequences have been followed. In the first sequence (Scheme 4, method 1), methyl 12-oxooc-tadecanoate [13], methyl 9- oxooctadecanoate [19], 1-hydroxy-12-octadecanone [20] or l-hydroxy-9-octadecanone [21] was dissolved in methanol and refluxed in the presence of hydroxylamine hydrochloride whereby triethylamine was used as a hydrochloric acid acceptor. When the reaction was complete, the triethylaminehy-drochloride salts were removed with water the oximes were extracted with hexane from the reaction mixture and isolated in a pure form as determined by NMR. One... 

Propylene oxide and 1,2-butylene oxide cyclic ethers find their largest use as chemical intermediates. Both oxides react readily with dilute amounts of mineral acids (e.g., hydrochloric acid) to form the chlorohydrin addition product. This reactivity with acid make these epoxy solvents valuable acid acceptor-type stabilizers for several chlorinated solvents. Trace amounts of hydrogen chloride from chlorinated solvent degradation is immediately neutralized by reaction with the propylene or 1,2-butylene oxide stabilizer. Reaction of propylene oxide with an alcohol or phenol in the presence of an acid catalyst yields the monoether of propylene glycol (see Chapter 13 for the glycol ethers). 

Epoxide resins, such as the widely used diglycidyl ether of bisphenol A, can be used in conjunction with sulphide accelerators as metal-oxide free curing systems. It would seem that the main function of the epoxide is as a hydrochloric acid acceptor with the accelerator acting as the curing agent. 

Maleimide. Maleimide and maleic anhydride are simple olefins and very useful molecules in organic syntheses for introducing various substituents. Addition reactions, cyclodimerization, Diels-Alder reactions and polymerization reactions are as well-known as their photochemical reactions. They are also known as electron acceptors in photoinduced electron-transfer reactions. The photosensitized reaction of maleimide with xanthone in 2-propanol has been investigated by TR EPR. The emissive CIDEP spectrum observed in 2-propanol is predominantly assigned to two kinds of maleimide alkyl-type radicals. On the other hand, the absorptive spectrum of the maleimide radical-anion was observed in 2-propanol in the presence of hydrochloric acid. The hydrochloric acid addition effect on the CIDEP patterns indicates the existence of two mechanisms for the photosensitization of maleimide by xanthone. One is a T-T energy transfer to maleimide followed by hydrogen abstraction by maleimide... 

The discoloration was found to be caused by trace amounts of hydrochloric acid which form when Neoprene oxidizes on aging. This acid reacts with iron to form ferric chloride, which in turn reacts with the thiuram disulfide modifier to form a black iron sulfide compound. Acid acceptors such as magnesia and zinc oxide were found to be effective in preventing this discoloration. However, their addition tended to decrease the viscosity stability of adhesive cements even further. 

For this reaction to proceed it is obviously necessary to remove the hydrochloric acid formed, preferably by means of hydrohalide acceptor. 

A1C13, or S02 in an inert solvent cause colour changes in indicators similar to those produced by hydrochloric acid, and these changes are reversed by bases so that titrations can be carried out. Compounds of the type of BF3 are usually described as Lewis acids or electron acceptors. The Lewis bases (e.g. ammonia, pyridine) are virtually identical with the Bransted-Lowry bases. The great disadvantage of the Lewis definition of acids is that, unlike proton-transfer reactions, it is incapable of general quantitative treatment. 

The hollow fiber was dipped into dihexyl ether for 5 sec and excess adhering solvent was washed away by ultrasonification in a water bath. Then, 25 fiL of lOmM hydrochloric acid (aqueous, acceptor phase) was injected into the lumen of the hollow fiber with a microsyringe. This activated fiber was placed in the vial containing the donor solution and the vial vibrated at 1500 rpm for 45 min. The entire acceptor solution was flushed into a 200-fJ.L micro insert and subjected to capillary electrophoresis or HPLC detection. For 2 mL extractions, 250 //I. of plasma sample treated with... 

The reaction of compound 98 with Michael acceptors such as acrylonitrile in the presence of pyridine gives a product which reveals to be the /3-(3-hydroazino-l,2,4-triazolo[3,4-A]benzothiazole)propanenitrile 203, which on reflux with hydrochloric acid underwent hydrolysis, followed by simultaneous cyclization, forming 3-(pyrazol-5-one-l-yl)-[l,2,4]triazolo[3,4-A]benzothiazole 204 (Scheme 10) <2004IJH241>. 

The acceptor properties of Ni2 + are weaker than those of Co2 + and under analogous conditions the extent of complex formation is smaller. When sodium azide is added to a 10 3 molar nickel (II) perchlorate solution in excess, the only azide-complex is monoazidonickel (II). The monochloro complex is present only in strong hydrochloric acid 81L Due to the low solvating properties of DMA even tetrachloronickelate (II) is found in such solutions. 

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