Potassium borohydride preparation

Other Borohydrides. Potassium borohydride was formerly used in color reversal development of photographic film and was preferred over sodium borohydride because of its much lower hygroscopicity. Because other borohydrides are made from sodium borohydride, they are correspondingly more expensive. Generally their reducing properties are not sufficiently different to warrant the added cost. Zinc borohydride [17611-70-0] Zn(BH 2> however, has found many appHcations in stereoselective reductions. It is less basic than NaBH, but is not commercially available owing to poor thermal stabihty. It is usually prepared on site in an ether solvent. Zinc borohydride was initially appHed to stereoselective ketone reductions, especially in prostaglandin syntheses (36), and later to aldehydes, acid haHdes, and esters (37). 

The tosylhydrazone is prepared from the carbonyl compound and then reduced with lithium aluminium hydride, sodium borohydride or potassium borohydride. In this way D-glucose tosylhydrazone was converted into crystalline 1-deoxyglucitol by reduction with potassium borohydride... 

Colloidal metals are usually prepared by reduction of a salt with a reducing agent, such as phosphorus, acetone, tannin, or carbon monoxide. Platinum metals can also be prepared as finely divided very active blacks by reducing the metal salt in an aqueous solution of sodium or potassium borohydride. 

Nickel borides are usually prepared by reduction of nickel salts with sodium or potassium borohydride. Two types are used. PI nickel boride is prepared by the reaction between aqueous solutions of nickel salts and a borohy-... 

Partial structures (lacking ring D ) of the bisindole alkaloids have been prepared by reaction of a substituted chloroimine with vindoline (21) under conditions that promote ionization to yield the coupled products as a mixture of diastereomers (59). Reaction of 27 with silver fluoroborate followed by addition of 21 gives 29 as a mixture of diastereomers in 49% yield. Treatment of this mixture with potassium borohydride under acid... 

Complex aluminum and boron hydrides can contain other cations. The following compounds are prepared by metathetical reactions of lithium aluminum hydride or sodium borohydride with the appropriate salts of other metals sodium aluminum hydride [55], magnesium aluminum hydride [59], lithium borohydride [90], potassium borohydride [9i], calcium borohydride [92] and tetrabutylammonium borohydride [95]. 

Potassium borohydride may be prepared by reacting potassium hydroxide with sodium borohydride. The salt precipitates from an aqueous solution of sodium borohydride with addition of potassium hydroxide ... 

Potassium borohydride also may be prepared by reacting potassium tetramethoxyborohydride with diborane at low temperatures or by passing diborane through a solution of potassium methylate in methanol. 

A method has been developed for the preparation of erythro- and threo-7-hydroxylated aporphines. Reduction of the A-metho-oxoaporphinium salt (42) with potassium borohydride resulted in a 60% yield of erythro-(43), whereas reduction with Adams catalyst followed by further treatment with borohydride gave erythro- 43) along with a minor amount of the rAreo-compound (44).47... 

Alternatively, the total carbonyl content of a lignin preparation may be determined by reduction with either sodium or potassium borohydride. This method is based on the Lindberg-Misiorny method for the determination of carbonyl groups in carbohydrates (Lindberg and Misiorny 1952, Lindberg and Theander 1954). Both sodium and potassium borohydrides are insoluble in ether but soluble in water without decomposition. At room temperature, they effectively reduce aldehydes and ketones in aqueous and methanol solutions, in particular in weakly alkaline solutions, without simultaneously reducing olefinic double bones ... 

The new selenacrown ether A,A -dimethyl-l,ll-diaza-4,8,14,18-tetraselenacycloicosane 32 has been synthesized and characterized <2005MI191>. Xu et al. have reported the first selenacrown and selenazacrown ethers bearing a hydroxy group. In this series, the key step is the preparation of the diselenide intermediate 188 by a reduction with potassium borohydride. It can then be condensed with dihalides or diol ditosylates 191 to give the aza 10-membered... 

An improved method for the preparation of selenacrown ethers has been described by Xu and co-workers. The synthesis of poly-(o-diselenobenzene) was detailed as the key intermediate for the syntheses of o-benzene diselenium type of selenacrown ethers. Under alkaline conditions, 5,6,1 l,12-tetraselena-dibenzo[tf/]cyclooctene 212 was reduced with potassium borohydride to give o-benzenediselenolate anion 213, which condensed with dihalides 215-217 and different 12- and 24-membered selenacrown ethers 218 and 219 were isolated in good yields (Scheme 31) C1995MI1559, 1997JCD1043, 1999JCD1039>. 

Potassium borohydride is a commercial product, but it can be prepared in a simple reaction from an aqueous solutionofNaBH4withpotassiumhydroxide (Eq. (5.8)) [24]. 

Lui et al. [8] prepared buclizine by reducing p-chlorophenyl phenyl ketone 1 with potassium borohydride to p-chlorobenzhydryl alcohol 2, which was converted into p-chlorobenzhydryl bromide 3. The latter compound 3 was prepared by reaction of p-chlorophenylmagnesium bromide 4 with benzaldehyde 5. p-ferf-Butylbenzyl chloride 6 was condensed directly with piperazine 7 to give p-ferf-butylbenzylpiperazine 8. Treatment of p-chlorobenzhydryl bromide 3 with p-ferf-butylbenzylpiperazine 8 in the presence of anhydrous sodium carbonate gave buclizine 9 hydrochloride. 

The approaches to quebrachamine adopted by other workers were rather different. Pakrashi and his collaborators (281) developed a synthesis via the known pentacyclic lactam 453 (prepared from 2-hydroxytryptamine and dimethyl 4-ethyl-4-formylpimelate) and 1,2-didehydroaspidospermid-ine (27), the final stage being simply the reduction of 27 by means of potassium borohydride, as in the last stage of the original synthesis of quebrachamine by Stork and Dolfini (Scheme 43). 

Epivoacristine (19-epivoacangarine) (mp 115° [a]p —55°inCHCl3) had spectrophotometric properties almost indistinguishable from voa-cristine (16). The only important difference was in the chemical shift, a doublet centered at 1.28 ppm (—CHOH-CHs) and found at 1.11 ppm in voacristine. This epi compound had previously been prepared by the potassium borohydride reduction of voacryptine (24). A conclusion as to the absolute configuration of the 19-hydroxyl was reached by using molecular rotation differences. 

Cathenamine (82) has been identified as an intermediate after strictosidine (79). The immonium salt.(80) lies logically between (79) and (82) see Scheme 3. Evidence in support has been obtained by isolating sitsikirine (91) and iso-sitsikirine (92) as new and exclusive products from a C. roseus enzyme preparation incubated with strictosidine (79) and potassium borohydride. (It would be interesting to repeat the experiment with borodeuteride and to determine the sites of labelling.)... 

Recently, a novel graphene-copper nanoparticle composite was prepared by the in situ chemical reduction of a mixture containing graphene oxides and copper(II) ions using potassium borohydride as a reductant. It was mixed with paraffin oil and packed into one end of the fused capillary to fabricate microdisk electrodes for sensing carbohydrates [14]. The results indicated that copper nanoparticles with an average diameter of 20.8 nm were successfully deposited on the graphenes to form a well-interconnected hybrid network. 

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