Brown procedure

In other reports, /i-cyclodextrins have been used to induce asymmetry in borohydride reduction of ketones, a diastereoselective reduction has been controlled by a n-allyltricarbonyliron lactone tether , a phosphinamide has been combined with a dioxaborolidine unit as an activated, directed catalyst for ketone reduction, reductive amination using benzylamine-cyanoborohydride converts 3-hydroxy ketones into syn-1,3-amino alcohols, l-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propan-1 -one has been reduced diastereoselectively, and production of chiral alcohols via (i) Itsuno-Corey and Brown procedures and (ii) lithium aluminium hydride modified by chiral nucleophiles has been reviewed. 

The Brown procedure for generating a fresh platinum catalyst uses NaBH< to reduce the Pt ... 

In an attempt to obtain more consistency with mass transfer theory, the transfer unit concept has been proposed. The number of gas-phase transfer units (Nqg) be calculated by the Souders and Brown procedure using the absorption factor [11]. This equation assumes linear, although not parallel, operating line and equilibrium curve. 

Muller K and Brown L D 1979 Location of saddle points and minimum energy paths by a constrained simplex optimization procedure Theor. Chim. Acta 53 75... 

The applicability of the two-parameter equation and the constants devised by Brown to electrophilic aromatic substitutions was tested by plotting values of the partial rate factors for a reaction against the appropriate substituent constants. It was maintained that such comparisons yielded satisfactory linear correlations for the results of many electrophilic substitutions, the slopes of the correlations giving the values of the reaction constants. If the existence of linear free energy relationships in electrophilic aromatic substitutions were not in dispute, the above procedure would suffice, and the precision of the correlation would measure the usefulness of the p+cr+ equation. However, a point at issue was whether the effect of a substituent could be represented by a constant, or whether its nature depended on the specific reaction. To investigate the effect of a particular substituent in different reactions, the values for the various reactions of the logarithms of the partial rate factors for the substituent were plotted against the p+ values of the reactions. This procedure should show more readily whether the effect of a substituent depends on the reaction, in which case deviations from a hnear relationship would occur. It was concluded that any variation in substituent effects was random, and not a function of electron demand by the electrophile. ... 

The MauIg Color Reaction. The procedure for this test consists basically of three sequential treatments of lignified material with 1% potassium permanganate, 3% hydrochloric acid, and concentrated ammonium hydroxide. A red-purple color develops for hardwoods and a brown color... 

Color. The visual color, from white to dark brown, of sugar and sugar products is used as a general indication of quaUty and degree of refinement. Standard methods are described for the spectrophotometric deterrnination of sugar color that specify solution concentration, pH, filtration procedure, and wavelength of deterrnination. Color or visual appearance may also be assessed by reflectance measurements. 

Acid—mordant dyes have characteristics similar to those of acid dyes which have a relatively low molecular weight, anionic substituents, and an affinity to polyamide fibers and mordant dyes. In general, brilliant shades caimot be obtained by acid—mordant dyes because they are used as their chromium mordant by treatment with dichromate in the course of the dyeing procedure. However, because of their excellent fastness for light and wet treatment, they are predominandy used to dye wool in heavy shades (navy blue, brown, and black). In terms of chemical constitution, most of the acid—mordant dyes are azo dyes some are triphenyhnethane dyes and very few anthraquinone dyes are used in this area. Cl Mordant Black 13 [1324-21 -6] (183) (Cl 63615) is one of the few examples of currentiy produced anthraquinone acid—mordant dyes. It is prepared by condensation of purpurin with aniline in the presence of boric acid, followed by sulfonation and finally by conversion to the sodium salt (146,147). 

Solutions in contact with polyvinyl chloride can become contaminated with trace amounts of lead, titanium, tin, zinc, iron, magnesium or cadmium from additives used in the manufacture and moulding of PVC. V-Phenyl-2-naphthylamine is a contaminant of solvents and biological materials that have been in contact with black rubber or neoprene (in which it is used as an antioxidant). Although it was only an artefact of the separation procedure it has been isolated as an apparent component of vitamin K preparations, extracts of plant lipids, algae, livers, butter, eye tissue and kidney tissue [Brown Chem Br 3 524 1967]. 

The experimental and theoretical procedure used by Tirrell et al. is similar to that of Brown and coworkers. Tirrell et al. compared their results from the JKR experiments to 90° peel tests. The details of the experiment may be obtained from the original papers. The obser ations of Tirrell et al. can be summarized as follows ... 

Note The reagent can be employed on silica gel and cellulose layers. The coloration of the stained chromatogram zones is dependent on the temperature and duration of heating. For instance, cholesterol appears bluish-pink after heating to 75 — 80 °C for 3 —5 min [1], but yellow to brown-colored after heating for 20 — 30 min (cf. Procedure Tested ). 

Reactions that occur with the development of an electron deficiency, such as aromatic electrophilic substitutions, are best correlated by substituent constants based on a more appropriate defining reaction than the ionization of benzoic acids. Brown and Okamoto adopted the rates of solvolysis of substituted phenyldimeth-ylcarbinyl chlorides (r-cumyl chlorides) in 90% aqueous acetone at 25°C to define electrophilic substituent constants symbolized o-. Their procedure was to establish a conventional Hammett plot of log (.k/k°) against (t for 16 /wcra-substituted r-cumyl chlorides, because meta substituents cannot undergo significant direct resonance interaction with the reaction site. The resulting p value of —4.54 was then used in a modified Hammett equation. 

A complete re-evaluation of a-values by statistical methods, as demanded in 1953, has been attempted by one of the present authors by a cumbersome interative procedure. This work was abandoned, however, when it was found that the resulting values were extremely sensitive to minor changes in the data used. Consequently, the carefully selected normal values of McDaniel and Brown, derived from... 

The acid catalyzed hydration of olefins is frequently attended by decomposition or rearrangement of the acid-sensitive substrate. A simple and mild procedure for the Markovnikov hydration of double bonds has recently been devised by Brown and co-workers 13). This reaction, which appears to be remarkably free of rearrangements, initially involves the addition of mercuric acetate to the double bond to give the 1,2-... 

It should be noted that although ASTM A262 1986 provides details of test procedures no information is given on typical corrosion rates or acceptable limits for various heat-treated alloys, which are regarded as outside the province of a specification that describes test procedures. Table 19.4, taken from a paper by Brown, shows the maximum acceptable evaluation test rates specified by the Du Pont Company for various alloys tested by the acid... 

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