In basic media

Carbon-oxygen bonds are formed by the Ullmann reaction (- coupling of aryl halides with copper) which has been varied in alkaloid chemistry to produce diaryl ethers instead of biaryls. This is achieved by the use of CuO in basic media (T. Kametani, 1969 R.W. Dos-kotch, 1971). 

Sulfenamidothiazoles are stable in basic media but decompose readily in acidic media to the disulfide and the amine (312). 

Disulfides (136) are formed in good yields by oxidation of A-4-thiazoline-2-thiones (135) and derivatives in basic media Scheme 69 (7, 130, 146-151, 317-319). 

Hydrolysis of TEOS in various solvents is such that for a particular system increases directiy with the concentration of H" or H O" in acidic media and with the concentration of OH in basic media. The dominant factor in controlling the hydrolysis rate is pH (21). However, the nature of the acid plays an important role, so that a small addition of HCl induces a 1500-fold increase in whereas acetic acid has Httie effect. Hydrolysis is also temperature-dependent. The reaction rate increases 10-fold when the temperature is varied from 20 to 45°C. Nmr experiments show that varies in different solvents as foUows acetonitrile > methanol > dimethylformamide > dioxane > formamide, where the k in acetonitrile is about 20 times larger than the k in formamide. The nature of the alkoxy groups on the siHcon atom also influences the rate constant. The longer and the bulkier the alkoxide group, the lower the (3). 

Vinyl chloride reacts with sulfides, thiols, alcohols, and oximes in basic media. Reaction with hydrated sodium sulfide [1313-82-2] in a mixture of dimethyl sulfoxide [67-68-5] (DMSO) and potassium hydroxide [1310-58-3], KOH, yields divinyl sulfide [627-51-0] and sulfur-containing heterocycles (27). Various vinyl sulfides can be obtained by reacting vinyl chloride with thiols in the presence of base (28). Vinyl ethers are produced in similar fashion, from the reaction of vinyl chloride with alcohols in the presence of a strong base (29,30). A variety of pyrroles and indoles have also been prepared by reacting vinyl chloride with different ketoximes or oximes in a mixture of DMSO and KOH (31). 

U/ .f-dimethylhydrazine is employed as a fuel in space appHcations. /V,/V-r)ichloroalkylamines can be converted to nitriles in basic media or by treatment with CsF in acetonitrile (69). 

Azolinones are protonated on oxygen in strongly acidic media. O-Alkylation of 2-azolinones can be effected with diazomethane thiazolinone (486) forms (487). Frequently O- and iV-alkylation occur together, especially in basic media where proton loss gives an ambident anion. 

V-Hydroxy groups can be acetylated (AC2O) and O-alkylated in basic media by methyl iodide. 1-Hydroxypyrazole 2-oxides are quite strong acids. 

Addition of hydride ion from the catalyst gives the adsorbed dianion (15). The reaction is completed and product stereochemistry determined by protonation of these species from the solution prior to or concurrent with desorption. With the heteroannular enolate, (13a), both cis and trans adsorption can occur with nearly equal facility. When an angular methyl group is present trans adsorption (14b) predominates. Protonation of the latter species from the solution gives the cis product. Since the heteroannular enolate is formed by the reaction of A" -3-keto steroids with strong base " this mechanism satisfactorily accounts for the almost exclusive formation of the isomer on hydrogenation of these steroids in basic media. The optimum concentration of hydroxide ion in this reaction is about two to three times that of the substrate. 

Because of the presence of alkali in Raney nickel, ketones are hydrogenated over this catalyst to yield the more stable, equatorial alcohol e.g. 59) as the predominant product, Similar results can be expected with platinum in basic media or with platinum oxide in an alcoholic solvent since this catalyst also contains basic impurities. 

Nickel peroxide is a solid, insoluble oxidant prepared by reaction of nickel (II) salts with hypochlorite or ozone in aqueous alkaline solution. This reagent when used in nonpolar medium is similar to, but more reactive than, activated manganese dioxide in selectively oxidizing allylic or acetylenic alcohols. It also reacts rapidly with amines, phenols, hydrazones and sulfides so that selective oxidation of allylic alcohols in the presence of these functionalities may not be possible. In basic media the oxidizing power of nickel peroxide is increased and saturated primary alcohols can be oxidized directly to carboxylic acids. In the presence of ammonia at —20°, primary allylic alcohols give amides while at elevated temperatures nitriles are formed. At elevated temperatures efficient cleavage of a-glycols, a-ketols... 

Hydrogenation of carbonyls, or incipient carbonyls such as phenols (86), in lower alcohol solvents may result in the formation of ethers. The ether arises through formation of acetals or ketals with subsequent hydrogenolysis. The reaction has been made the basis of certain ether syntheses (45,97). Reaction of alcohols with carbonyls may be promoted by trace contamination, such as iron in platinum oxide (22,53), but it is also a property of the hydrogenation catalyst itself. So strong is the tendency of palladium-hydrogen to promote acetal formation that acetals may form even in basic media (61). 

Problem 22.9 Why do you suppose ketone halogenations in acidic media referred to as being ackl-calalyzed, whereas halogenations in basic media are base-promoted In other words, why is a full equivalent of base required for halogenation ... 

Such direct cyclizations usually occur in basic media to afford quinoxaline A-oxides. For success, C2 in the ethyl group needs to be a carbonyl entity or to be suitably activated. The following examples illustrate this valuable route to such A-oxides (and thence to quinoxalines see Section 4.6.2.1). 

The polyanhydrides in general degrade more rapidly in basic media than in acidic media (4). This effect is shown in Fig. 2. 

A study of the decomposition in basic media of the erythro- and threo-isomers of the /8-hydroxyphosphonate (169) showed that the first step in the phosphonate olefin synthesis is reversible and that the diastereo-isomers of (169) can also interconvert directly, presumably via the a-car-banion. 

Approximate ratios of the velocity constants for the hydrolysis in basic media of di- and monoesters of homologous dibasic acids are given in the second column of Table The logarithm of this ratio,... 

Cobalt(II) complexes of 4-(2-thiazolyl)-l-(2-acetylfuran) thiosemicarbazone, 44, were isolated having stoichiometries of [Co(44)2Cl2] and [Co(44-H)2] [194]. The former complex is isolated from neutral solution and is octahedral with each 44 bonding NS. The latter complex is formed in basic media, involves a tetrahedral cobalt(II) center and has NS bonding based on infrared studies. 

Kim J, Gewirth A. 2006. Mechanism of oxygen electroreduction on gold surfaces in basic media. J Fhys Chem B 110 2565-2571. 

Chemical shift in acidic media is defined as at pH <2.0. Chemical shift in basic media is defined as at pH >11.0 for more details, see Ref. 23. b C of N-terminal glycine exhibited pH-dependence at pH >7.0. C of C-terminal glycine exhibited pH-dependence at pH <7.0. 

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