Bases, Table

Few representative dyes of cyanine base (Table 2114) resulting from the condensation of alkylmercapto indolenine on 2-methylthiazoliurn have been described. 

With samples that are difficult to dissolve, the first approach is usually to try digesting the sample with an acid or base. Table 7.2 lists the most commonly used acids and bases and summarizes their use. Digestion is commonly carried out in an open container, such as a beaker, using a hot plate as a source of heat. The chief advantage of this approach is its low cost as it requires no special equipment. Volatile reaction products, however, are lost, leading to a determinate error if analyte is included among the volatile substances. 

Abbott Laboratories, which has conducted additional toxicity and carcinogenicity studies with cyclamate, a 10 1 mixture of cyclamate—saccharin, and cyclohexylamine, claimed to be unable to confirm the 1969 findings. Abbott then filed a food additive petition for cyclamate in 1973, which was denied by the FDA in 1980. In 1982, the Calorie Control Council and Abbott Laboratories filed a second food additive petition containing the results of additional safety studies (73). That petition was stiU pending as of 1996. Cyclamate is, however, allowed for use in any or all three categories, ie, food, beverage, and tabletop, in about 50 countries. Sweet n Low, known in the United States as a saccharin-based table-top sweetener, contains exclusively cyclamate in Canada. 

Commercially, the most important fast color bases (Table 10) and salts include Azoic Diazo Component 3, produced by the reduction of... 

This procedure is representative of a new general method for the preparation of noncyclic acyloins by thiazol ium-catalyzed dimerization of aldehydes in the presence of weak bases (Table I). The advantages of this method over the classical reductive coupling of esters or the modern variation in which the intermediate enediolate is trapped by silylation, are the simplicity of the procedure, the inexpensive materials used, and the purity of the products obtained. For volatile aldehydes such as acetaldehyde and propionaldehyde the reaction Is conducted without solvent in a small, heated autoclave. With the exception of furoin the preparation of benzoins from aromatic aldehydes is best carried out with a different thiazolium catalyst bearing an N-methyl or N-ethyl substituent, instead of the N-benzyl group. Benzoins have usually been prepared by cyanide-catalyzed condensation of aromatic and heterocyclic aldehydes.Unsymnetrical acyloins may be obtained by thiazol1um-catalyzed cross-condensation of two different aldehydes. -1 The thiazolium ion-catalyzed cyclization of 1,5-dialdehydes to cyclic acyloins has been reported. 

The rate of reaction of a series of nucleophiles with a single substrate is related to the basicity when the nucleophilic atom is the same and the nucleophiles are closely related in chemical type. Thus, although the rates parallel the basicities of anilines (Tables VII and VIII) as a class and of pyridine bases (Tables VII and VIII) as a class, the less basic anilines are much more reactive. This difference in reactivity is based on a lower energy of activation as is the reactivity sequence piperidine > ammonia > aniline. Further relationships among the nucleophiles found in this work are morpholine vs. piperidine (Table III) methoxide vs. 4-nitrophenoxide (Table II) and alkoxides vs. piperidine (Tables II, III, and VIII). Hydrogen bonding in the transition state and acid catalysis increase the rates of reaction of anilines. Reaction rates of the pyridine bases are decreased by steric hindrance between their alpha hydrogens and the substituents or... 

Quinoxalin-2-ones are in tautomeric equilibrium with 2-hydroxy-quinoxalines, but physical measurements indicate that both in solution and in the solid state they exist as cyclic amides rather than as hydroxy compounds. Thus quinoxalin-2-one and its A -methyl derivative show practically identical ultraviolet absorption and are bases of similar strength. In contrast, the ultraviolet spectra of quinoxalin-2-one and its 0-methyl derivative (2-methoxyquinoxaIine) are dissimilar. The methoxy compound is also a significantly stronger base (Table II). Similar relationships also exist between the ultraviolet absorption and ionization properties of 3-methylquinoxalin-2-one and its N- and 0-methyl derivatives. The infrared spectrum of 3- (p-methoxy-benzyl)quinoxalin-2-one (77) in methylene chloride shows bands at 3375 and 1565 cm" which are absent in the spectrum of the deuterated... 

As a result of alkylation LAB is obtained with a clearly changed composition in comparison with the use of chloroparaffin. With respect to the dialkyl-tetralin content, values are obtained which are comparable to LAB from the HF alkylation process (same olefin base) (Table 11). Another important difference is the 2-phenylalkane content. The isomer distribution depends on the catalyst. The reaction between straight /z-chloroparaffins or n-olefins with benzene in the presence of aluminum chloride leads to the same isomer distribution. In both cases the 2-phenylalkane content is predominant compared to the 3-, 4-, and 5-phenylalkanes. If hydrogen fluoride is used as catalyst the 2-phenylalkane... 

Identify common strong acids and bases (Table J.l). 

Besides water, the most common weak base is ammonia, NH3, whose proton transfer equilibrium with water appears in Section 16-. Many other weak bases are derivatives of ammonia called amines, hi these organic compounds, one, two, or three of the N—H bonds in ammonia have been replaced with N—C bonds. The nitrogen atom in an amine, like its counterpart in ammonia, has a lone pair of electrons that can form a bond to a proton. Water does not protonate an amine to an appreciable extent, so all amines are weak bases. Table 17-4 lists several examples of bases derived from ammonia. 

In the last two sections we have described several different categories of strong and weak acids and bases. Table 17-5 summarizes the characteristics of these species. 

We have calculated several approximations of the energy of (ground electronic state) using various GTO bases (Table 1). In all cases the intcrnuclear distance used was equal to 2 B, close to the experimental equilibrium distance (Re=1.98 B (10))... 

Interestingly, the scope of the reaction using this catalyst can be extended to oxidative kinetic resolution of secondary alcohols by using (-)-sparteine as a base (Table 10.2) [25]. The best enantiomeric excess of the alcohol was obtained when a chiral enantiopure base and an achiral catalyst were used. The use of chiral enantiopure catalyst bearing ligand 17 led to low enantioselectivity. 

The above treatment of moderately dilute acids and dibasic acids can be used for analogous cases of bases. Table 1.7 lists examples of dissociation constants of bases in aqueous solutions. 

Evidence-Based Table of Selected Treatment Recommendations Variceal Bleeding in Portal Hypertension... 

As was pointed out in the previous chapter, biologically important metal ions and their ligands can be classified according to the hard-soft theory of acids and bases (Table 2.1). While there are exceptions, most metal ions bind to donor ligands as a function of preferences based on this concept, with hard acids (metal ions) binding preferentially to hard bases (ligands) and soft acids to soft bases. 

Table-top sweeteners must be named. . -based table-top sweetener , including the name(s) of the sweetener(s) used. 

For comparison, fluorous-phase-soluble Pd complexes are only 74-98% selective towards the trans product [168-170]. The isolated yields of the product approached 70% when a threefold excess of olefin to iodobenzene was used (Table 3) however, the percent yield decreased with the use of bromobenzene as expected since activation of bromine-carbon bonds is less favorable than iodo-carbon bonds. It was also possible to catalyze the reaction in the absence of additional triethylamine base (Table 3). In this case, the tertiary amines of the den-drimer most likely act as the base. The catalysts, in general, were fully recover-... 

The authors proposed that the Brpnsted base interaction on the catalyst is imperative for reactivity. Catalysts lacking a basic amine moiety, specifically mono- and bis-ureas, did not promote the asymmetric catalytic addition well, if at all. In screening a variety of amine bases and bis-ureas, it became apparent that presence of a Brpnsted base was necessary for catalytic activity (Scheme 61) [113]. The reactivity was extremely low in absence of Brpnsted base (Table 2, entry 2), but slightly improved with presence of NEtj (Table 2, entry 1). Combined, a chiral Brpnsted acid and Brpnsted base increase conversion and showed some enantiose-lectivity (Fig. 8). 

Focused X-ray beam (at Beam Line 15A) was used for this study. In order to improve the resolution, the focused beam (about 1 x 1.5 mm) was cut into 0.9-0.5 mm O by apertures which were set just in front of the cell. Modulation frequency was 10 Hz. Scanning X-Y stage which was originally developed for the laser microscopy was set perpendicular to the surface of the iron-base table and scanning and data acquisition were controlled by PC-9801 VM2 microcomputer (NEC Co. Ltd.) with the original program Various size and shape of metal foils were glued on the paper to have a model patterned sample. 

The nitrogen of 2/7-dihydrothiazines reacts readily with alkyl or acyl halides in the presence of a base. Table 8 contains a selection of N-alkylations and N-acylations performed on dihydro-1,4-thiazine derivatives. 

Affinity coefficient / based Table 1.22 on the molar volumes for selected compounds ... 

Like vinylogous ketol to ketol rearrangements (Section 3.2.4.5.), ketol to ketol rearrangements can be induced by treatment with acids, but are most often brought about by treatment with base. However, only a few examples exist where the rearrangement leads to enlargement of a three-membered ring.195 199 Of these cases, 5-hydroxybicyclo[3.2.0]heptan-6-ones were effectively produced by treatment of l-hydroxybicyclo[4.1.0]heplan-2-ones with base (Table 17).197-199... 

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