Base or acid treatment

Ring expansion reactions are much better known and sulfolene substrates have received considerable investigation. Cyclopropanation with dichlorocarbene affords 6,6-dichloro-3-thiabicyclo[3.1.0]hexane 3,3-dioxides which may readily be ring enlarged by base or acid treatment. Base treatment, especially with LDA, cleanly affords 2//-thiopyran dioxides hydrochloric acid does likewise, but less cleanly, while hydrobromic acid treatment causes a more complex set of reactions leading to thiopyranones containing bromine in which the sulfur has been reduced. The intermediacy of thiopyrylium oxides has been invoked to rationalize the observations (Scheme 27) (81JOC4502). 

Upon [2 + 2]-photocycloaddition to product E and protecting group removal, the retro-aldol fragmentation can be initiated by base or acid treatment (Scheme 6.18). Under basic conditions, alkoxide F generates an enolate which is subsequently protonated to the 1,5-diketone G. 

Table 8.7 shows the 02/N2and CO2/CH4 permeance ratio for the as-cast P3AcET membrane and the base- or acid-treated membrane. As the table shows, the base or acid treatment resulted in a dramatic increase in the O2/N2 permeance ratio, while... 

Dihydroxyquiaolines are found ia nature and may be prepared synthetically. Heating 3,l-benzoxazia-4-ones with strong base or sequential treatment of A/-acetoacetylanthranilate with base, then acid, produce 2,4-dihydroxyquiQolines [70254-43-2] (127,128). An enzymatic preparation of 4,5-dihydroxyquiQoline has been reported (129). 

Acylglycerols can be hydrolyzed by heating with acid or base or by treatment with lipases. Hydrolysis with alkali is called saponification and yields salts of free fatty acids and glycerol. This is how soap (a metal salt of an acid derived from fat) was made by our ancestors. One method used potassium hydroxide potash) leached from wood ashes to hydrolyze animal fat (mostly triacylglycerols). (The tendency of such soaps to be precipitated by Mg and Ca ions in hard water makes them less useful than modern detergents.) When the fatty acids esterified at the first and third carbons of glycerol are different, the sec-... 

These alkene isomers are separately available (4) by treatment of threo-S-trimethylsilyloctan-4-ol, prepared by reduction of the corresponding ketone with DIBAL in pentane at —120°C, with base or acid. The preparation of 5-trimethylsilyloctan-4-one itself illustrates three general procedures the addition of alkyl lithium reagents to vinylsilanes to generate a-lithiosilanes, the preparation of complex /5-hydroxysilanes, as diastereoisomeric mixtures, and the oxidation of such compounds to /8-ketosilanes... 

The popular methodology for the construction of carbocyclic ring consists of the intramolecular aldol condensation of properly activated monosugars. This may be exemplified by transformation of 73 into the dicarbonyl derivative 74 which, upon treatment with base (or acid), provided the desired carbocycle (Fig. 26).39 Other differently substituted derivatives were also prepared by this approach.40... 

Protection of Alcohols. Trimethylsilyl ethers, readily prepared from alcohols by treatment with a variety of silylating agents have found considerable use for the protection of alcohols. They are thermally stable and reasonably stable to many organometallic reagents and they are easily cleaved by hydrolysis in acid or base or by treatment with fluoride ion. t, Butyl dimethylsilyl ethers have considerably greater hydrolytic stability and are easier to work with than trimethylsilyl ethers. They are prepared from alcohols by treatment with t. butyl dimethylsilyl chloride. 

The reaction of acceptor-substituted carbene complexes with alcohols to yield ethers is a valuable alternative to other etherification reactions [1152,1209-1211], This reaction generally proceeds faster than cyclopropanation [1176], As in other transformations with electrophilic carbene complexes, the reaction conditions are mild and well-suited to base- or acid-sensitive substrates [1212], As an illustrative example, Experimental Procedure 4.2.4 describes the carbene-mediated etherification of a serine derivative. This type of substrate is very difficult to etherify under basic conditions (e.g. NaH, alkyl halide [1213]), because of an intramolecular hydrogen-bond between the nitrogen-bound hydrogen and the hydroxy group. Further, upon treatment with bases serine ethers readily eliminate alkoxide to give acrylates. With the aid of electrophilic carbene complexes, however, acceptable yields of 0-alkylated serine derivatives can be obtained. 

The oxidation of 3H- 1,2-benzodiazepines (90 R = Hor Me) with MCPB A gave both (91) and (92). The former have proved useful as precursors for 3-substituted 1,2-benzodiazepines via treatment with bases or acids. Thus (91) on reaction with alkoxides (R -) and CH(C02Et)2 gave respectively (93 X = OR1) and (93 X = CH(C02Et)2) in ca. 70% yields, and treatment with hydrogen chloride and with acetic acid gave (93 X = C1) and (94) respectively (78CPB1896). 

Several epoxy eugaxe containing a euitably dispoeed free hydroxyl group have been shown to yield new anhydro sugars on treatment with aqueous base or acid. When the free hydroxyl group ict on a carbon atom... 

Dilute aqueous streams are sent to waste-water treatment unless the contaminants are toxic to the bacteria in the waste-water plant. Acidic or basic wastes are neutralized prior to treatment. Neutralization is usually carried out using a base or acid that will form a solid salt that can be precipitated from the water so that the total dissolved solids (TDS) load on the waste-water plant is not excessive. The cost of waste-water treatment is typically about 6 per 1,000 gal ( 1.5 per metric ton), but there may also be local charges for spent water discharge. 

The detoxification of catalysts poisoned by Group V or VI compounds can be accomplished by reactions in which these inhibitors are converted to substances that do not have unshared electron pairs. For instance, bivalent sulfur compounds can be oxidized to sulfones or sulfonic acids by treatment with hypochlorite or hydroperoxides. "2,108 Thiophene, dimethyl sulfide and other sulfur and metal ion poisons as well as phosphorous"" and arsenic compounds " can be removed from platinum by washing the catalyst with acetic acid. This method for the reactivation of the catalyst is simpler than the oxidation techniques. Acidic or basic inhibitors are removed by the addition of an appropriate amount of base or acid, respectively. The effect of a small amount of inhibitor can frequently be overcome by the use of a larger amount of catalyst. 

Phosphorus oxychloride is a suitable reagent for preparation of the symmetrically substituted phospho-triesters of type (RO)3PO. The preparation is easily achieved by treatment of phosphorus oxychloride with 3 equiv. of alcohols or their metal salts. The reaction is generally promoted by a base or acid. Titanium trichloride is a particularly effective catalyst for the reaction. Conversion of POCI3 to unsymmetri-cally substituted phosphotriesters is achievable with difficulty. Phosphorochloridates and phosphorodichloridates have been used for the preparation of mixed tertiary phosphoric esters of type (ROlmPOfOROn (ffi = 1, n = 2, or m = 2, n = 1) in a very wide variety. Reaction of phosphorus oxychloride and 1 or 2 equiv. of alcohols followed by hydrolysis forms phosphomonoesters or phosphodi-esters, respectively. The hydrolysis may be generally effected by dilute aqueous alkali. Some phosphoFodichlori te intermediates are easily hydrolyzed by water. For example, the phosphorylation of a ribonucleoside (1 equation 4) with phosphorus oxychloride in an aqueous pyridine-acetonitrile mixture furnishes the nucleoside S -monophosphate (2) in excellent yield. ... 

The tetracyclines are amphoteric antimicrobial agents that can form salts with bases or acids (see Chs 1 and 2). Oxytetracycline is a bitter, yellow, odorless crystalline powder. The base is slightly water soluble and the hydrochloride is readily water soluble and is typically administered to horses by slow i.v. injection. It is effective at 5.5 mg/kg once daily for 2 days or more in the treatment of B. equi but is unlikely to completely clear this infection. It is, therefore, used for premunition. Rapid i.v. injection may cause a precipitous drop in blood pressure and collapse owing to the effects of calcium chelation on the myocardium. Intramuscular injection causes objectionable local reactions in horses and should be avoided. Oral administration may be more... 

Neutralization titrations are used to determine the innumerable inorganic, organic, and biological species that possess inherent acidic or basic properties. Equally important, however, are the many applications that involve conversion of an analyte to an acid or base by suitable chemical treatment followed by titration with a standard strong base or acid. 

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