Solvents, organic, basic

Since the second solvent pair fall within the poor hydrogen bonding group of solvents, increased basicity of the organic base in these solvents would be consistent with the observed behavior. Based on the model compound studies, indications are that the base-catalyzed imidization process may involve a two-step mechanism, Jee Scheme 23. The first step corresponds to the complete or partial proton abstraction from the amide group with the formation of an iminolate anion. Since this iminolate anion has two possible tautomers, the reaction can proceed in a split reaction path to either an isoimide- or imide-type intermediate. Although isoimide model reactions indicate an extremely fast isomerization to the imide under the conditions employed for base-catalysis, all indications to date are that it is not an intermediate in the base-catalyzed imidization of amic alkyl esters. 

Solvent dyes [1] cannot be classified according to a specific chemical type of dyes. Solvent dyes can be found among the azo, disperse, anthraquinone, metal-complex, cationic, and phthalocyanine dyes. The only common characteristic is a chemical structure devoid of sulfonic and carboxylic groups, except for cationic dyes as salts with an organic base as anion. Solvent dyes are basically insoluble in water, but soluble in the different types of solvents. Organic dye salts represent an important type of solvent dyes. Solvent dyes also function as dyes for certain polymers, such as polyacrylonitrile, polystyrene, polymethacrylates, and polyester, in which they are soluble. Polyester dyes are principally disperse dyes (see Section 3.2). 

Evolving enzymes with specific properties (e.g., higher activity in organic solvents) is basically a search process in the enzyme space (see Chapter 6 for a more detailed discussion). Onereasonwhy directed evolution outperforms rational design is the sheer size of this space. Since enzymes are made of 20 amino adds, even the sequence of a short enzyme containing just 80 amino acids can already have 2080 permutations. 

Erythromycin is, like penicillin, isolated by solvent-extraction methods. It is an organic base, and extractable with amyl acetate or other organic solvents under basic conditions rather than the acidic ones that favor penicillin extraction. 

Because of the rather localized negative charge at the phenoHc oxygen atom , the standard dye (44) is capable of specific HBD/HBA and Lewis acid/base interactions. Therefore, in addition to the nonspecific dye/solvent interactions, the betaine dye (44) predominately measures the specific HBD and Lewis acidity of organic solvents. On the other hand, the positive charge of the pyridinium moiety of (44) is delocalized. Therefore, the solvent Lewis basicity will not be registered by the probe molecule (44). If this solvent property is relevant for the system under study, other empirical measures of Lewis basicity should be used cf. Section 7.7. 

However, the model proposed by Behr and coworkers [220, 292] cannot explain the change in the rate of electrode reactions occurring in binary mixtures of water with solvents more basic than water. Instead of a decrease of the rate with an increase of the organic component, an increase of the rate is expected for ion-transfer reactions. Experimentally such a maximum has never been observed [293]. One should also add that basic properties of solvent molecules adsorbed on the electrode surface may be quite different from those of bulk molecules. 

Because it is not an oxidizing agent, concentrated hydrochloric acid is normally not used to digest organic materials. Nevertheless, it is an effective solvent for basic compounds such as amines and alkaloids in aqueous solutions, as well as for some organometallic compounds. The hydrolysis of natural products with HCl is a routine preliminary procedure for the analysis of amino acids and carbohydrates. 

Properties Colorless liquid faint amine odor. D 0.913-0.919 (15/15C), bp 256C, fp -0.1C, refr index 1.4823 (25C), flash p 210F (98.9C). Slightly soluble in water miscible with organic solvents. Strongly basic. 

Organic Solvent. The organic phase consists of two or three components reagent, modifier, and solvent. A basic study of possible chemicals for these components dates back to 1960 [5.33],... 

Another notable difference between the Zr-catalyzed ethylmagnesations of allylic ethers and alcohols is the effect of solvent Lewis basicity on reaction selectivity. Thus, as iUustrated in Scheme 3.79, whereas reactions with allylic ethers are entirely insensitive to variations in solvent structure, those of allylic alcohols are strongly influenced. These observations led Hoveyda and coworkers to conclude that for allylic alcohols (allyhc alkoxides after rapid deprotonation by the Grignard reagent) there is chelation between the Lewis basic heteroatom and a metal center (Zr or Mg) this association, which gives rise to transition state organization and high diastereocon-trol, is altered in the presence of Lewis basic THF, with diminution in selectivity. 

Most of the recent isolation studies have used fresh plant materials. Under these conditions the yield of crude alkaloids may approach 1% but usually is less than half of this value. When the crystalline alkaloid have been separated from each other and the amorphous fractions, an abundant alkaloid usually is present to the extent of 0.01% to 0.1%. At the other extreme, modem isolation techniques have made possible the isolation of pure alkaloids which represent only 0.0001% of the fresh plant weight. After conventional extractions of the ground plant material with an organic solvent, the basic fraction is transferred to an aqueous phase with dilute acid, and the nonbasic material is removed by extraction with an immiscible solvent. Considerable care must be exercised at this point since the hydrochlorides of the lactonic and nonhydroxylic alkaloids often are soluble in chloroform. Unlike the majority of alkaloids in the family, lycorine is practically insoluble in ethanol or chloroform and may be separated with ease from most alkaloid mixtures. Final isolation of pure alkaloids is achieved through differences in solubility, basicity, or adsorptivity on alumina. A method for the separation of the alkaloids by paper chromatography has been described (63a). Table 2 records the members of the Amaryllidaceae which have been examined for alkaloids up to November, 1958. Typical isolations are described below. 

At the beginning of this Chapter we have mentioned that one of the oldest methods for isolation of organic natural products is extraction. Primary metabolites discussed up to now were mainly ionic or polar compounds soluble in water or in polar solvents. Organic natural products that belong to different structural classes but which have in common the solubility in nonpolar solvents are called lipids. Some of the hpids are esters of long-chained fatty acids and they can be readily hydrolyzed under acidic or basic conditions. In this group we encounter waxes, fats and phospholipids. 

Basic dyes are water-soluble in the form of their salts and are used for colouring paper, leather, cellulose- and polyacrylonitrile fibres. The free bases dissolve in many organic solvents and find application similar to that of the solvent dyes. Basic dyes can function as pigments in lacquer form. Mixtures of basic dyes are usually responsible for brown, green and black tones. 

One important class of block copolymers are amphiphilic block copolymers that have affinities for two different environments. These two blocks interact very differently with the environment due to their chemical nature, and they behave distinctively in solution. The aforementioned differences can induce microphase separation of an amphiphilic block both in aqueous media and in organic solvents. Two basic processes can be distinguished for block copolymers in solvent media, namely micellization and gelation. Micellization occurs when the block copolymer is dissolved in a large amount of a selective solvent for one of the blocks. In this case, the polymer chains tend to organize themselves in a diversity of structures, from... 

The preparation of salts of organic acids with amines is identical in principle for all organic acids. Suitable amounts of a base and of the acid are mixed in a suitable solvent, and the mixture is allowed to crystallize. As for the choice of solvent, the basicity of the amine should be respected. Therefore, the salts of less-basic amines are prepared in less-polar solvents. The solvents used are water, ethanol methanol, ethyl acetate (for picrates), ether, chloroform, and benzene. It is evident that when choosing the solvent the solubilities of the amine and the acid, and of the salt as well, should be taken into consideration. 

CMC, anionic cellulose ether, is available in a variety of types based on particle size, DS, viscosity and hydration characteristics for different food applications. It is soluble in hot and cold water but insoluble in organic solvents. It basic function is to bind water or impart viscosity to the aqueous phase thereby stabilizing the other ingredients or preventing... 

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