Insolubility water

M.p. 222 C. Soluble in water, insoluble in alcohol. Citrulline is an intermediate in the urea cycle in the excretion of excess nitrogen from the body. 

H2N-CH2 [CH2j3.CH(NH2) COOH. Colourless needles, m.p. 224 C (decomp.), very soluble in water, insoluble in alcohol. L-(-H)-Lysine is one of the basic amino-acids occurring in particularly large quantities in the protamine and histone classes of proteins. It is an essential amino-acid, which cannot be synthesized by the body and must be present in the food for proper growth. It can be manufactured by various fermentation processes or by synthesis. 

S = solid, A = air, W = water or aqueous phase, O = oily or organic water-insoluble phase.)... 

An emulsion may be defined as a mixture of particles of one liquid with some second liquid. The two common types of emulsions are oil-in-water (O/W) and water-in-oil (W/0), where the term oil is used to denote the water-insoluble fiuid. These two types are illustrated in Fig. XIV-1, where it is clear that the majority or outer phase is continuous, whereas the minority or inner phase is not. These two emulsion types are distinguished by their ability to disperse oil or water-soluble dyes, their dilution with oil or water, and their conductivity (O/W emulsions have much higher conductivity than do W/0 ones see Ref. 1 for reviews). 

Plenary 3. Ronald E Hester et al, e-mail address reh York.ac.uk (SERS). Use of dioxane envelope to bring water insoluble cliromophores (chlorophylls) into contact with aqueous silver colloids for SERS enliancement. PSERRS— protected surface-enhanced resonance Raman spectroscopy . 

Steam-distillation. Many water-insoluble compounds, both solid and liquid, may be readily purified by distillation in a... 

If the organic compound which is being steam-distilled is freely soluble in water, an aqueous solution will ultimately collect in the receiver F, and the compound must then be isolated by ether extraction, etc. Alternatively, a water-insoluble compound, if liquid, will form a separate layer in F, or if solid, will probably ciystallise in the aqueous distillate. When steam-distilling a solid product, it is sometimes found that the distilled material crystallises in E, and may tend to choke up the condenser, in such cases, the water should be run out of the condenser for a few minutes until the solid material has melted and been carried by the steam down into the receiver. 

To a few drops of formalin solution add a few drops of dinitro-phenylhydrazine reagent A (p. 263) a yellow precipitate is produced in the cold. Acetaldehyde and acetone give orange-coloured precipitates. Dissolve water-insoluble compounds e.g-y benzaldehyde, salicylalde-hyde, acetophenone and benzophenone) in a small volume of methanol before adding reagent B. With benzophenone the precipitate forms slowly. 

In the separations (2) and (3) above, it is often advisable to dissolve the original mixture in a water-insoluble solvent. Select a solvent which will dissolve the entire mixture, and then shake the solution with either (i) dil. NaOH or (ii) dil. HCl. Separate the aqueous layer, and to it add either (i) dil. HCl or (ii) dil. NaOH to liberate the organic acid or the organic base, as the case may be. The non-aqueous layer now contains the neutral component. Reextract this layer with either (i) dil. NaOH or (ii) dil. HCl to ensure removal of traces of the non-neutral component. 

To carry out a steam distillation, the solution (or mixture or the solid with a little water) is placed in the flask B, and the apparatus is completely assembled. Steam is passed into the flask B, which is itself heated by means of a small flame to prevent too rapid an accumulation of water, at such a rate that it is completely condensed by the condenser C. The passage of steam is continued until there is no appreciable amount of water-insoluble material in the distillate. If the substance crystallises... 

Dilute sodium hydroxide solution (and also sodium carbonate solution and sodium bicarbonate solution) can be employed for the removal of an organic acid from its solution in an organic solvent, or for the removal of acidic impurities present in a water-insoluble solid or liquid. The extraction is based upon the fact that the sodium salt of the acid is soluble in water or in dilute alkali, but is insoluble in the organic solvent. Similarly, a sparingly soluble phenol, e.g., p-naphthol, CioH,.OH, may be removed from its solution in an organic solvent by treatment with sodium hydroxide solution. 

For water insoluble aldehydes or ketones, the following alternative procedure may be used. Reflux a mixture of 0-6 g. of the aldehyde or ketone, 0 5 g. of hydroxylamine hydrochloride, 5 ml. of ethanol and 0 5 ml. of pyridine on a water bath for 15-60 minutes. Remove the alcohol either by distillation (water bath) or by evaporation of the hot solution in a stream of air (water pump). Add 5 ml. of water to the cooled residue, cool in an ice bath and stir until the oxime crystallises Filter off the solid, wash it with a little water and dry. Recrystallise from alcohol (95 per cent, or more dilute), benzene, or benzene - light petroleum (b.p. 60-80°). 

For those nitriles which yield water-insoluble amides e.g., the higher alkyl cyanides), hydrolysis to the amide often leads to a satisfactory derivative. The hydration is eflfected by warming a solution of the nitrile in concentrated sulphuric acid for a few minutes, cooling and pouring... 

Most polysaccharides are insoluble or sparingly soluble in cold water, insoluble in cold alcohol and ether, and rarely possess melting points. Only inuUn melts at about 178° (dec.) after drying at 130°. 

Group II. The classes 1 to 5 are usually soluble in dilute alkali and acid. Useful information may, however, be obtained by examining the behaviour of Sails to alkaline or acidic solvents. With a salt of a water-soluble base, the characteristic odour of an amine is usually apparent when it is treated with dilute alkali likewise, the salt of a water soluble, weak acid is decomposed by dilute hydrochloric acid or by concentrated sulphuric acid. The water-soluble salt of a water-insoluble acid or base will give a precipitate of either the free acid or the free base when treated with dilute acid or dilute alkali. The salts of sulphonic acids and of quaternary bases (R4NOH) are unaflFected by dilute sodium hydroxide or hydrochloric acid. 

Group V. This group includes all the water-insoluble hydrocarbons and oxygen compounds that do not contain N or S and are soluble in cold concentrated sulphuric acid. Any changes—colour, excessive charring, evolution of gases or heat, polymerisation and precipitation of an insoluble compound— attending the dissolution of the substance should be carefully noted. 

In qualitative organic analysis, use is made of the fact that silver iodate is sparingly soluble in dilute nitric acid whereas silver periodate is very soluble. For water-insoluble compounds solutions in ethanol or in pure dioxan may be employed. 

An indication whether a water-insoluble compound is an acid or a phenol (or enol) will be obtained from the Solubihty Tests water-soluble acids will bberate carbon dioxide from 5 per cent, sodium bicarbonate solution see Section III,85,(i). ... 

The presence of simple water-insoluble phenols (or enols) will be indicated by the insolubility in 5 per cent, sodium bicarbonate solution. Further evidence will be obtained by carrying out the following tests. 

Esters of sulphuric acid. These compounds are generally water insoluble liquids and are saponified by boiling with water or dilute alkali to the corresponding alcohols and sulphuric acid ... 

Separations based upon differences in the chemical properties of the components. Thus a mixture of toluene and anihne may be separated by extraction with dilute hydrochloric acid the aniline passes into the aqueous layer in the form of the salt, anihne hydrochloride, and may be recovered by neutralisation. Similarly, a mixture of phenol and toluene may be separated by treatment with dilute sodium hydroxide. The above examples are, of comse, simple apphcations of the fact that the various components fah into different solubihty groups (compare Section XI,5). Another example is the separation of a mixture of di-n-butyl ether and chlorobenzene concentrated sulphuric acid dissolves only the w-butyl other and it may be recovered from solution by dilution with water. With some classes of compounds, e.g., unsaturated compounds, concentrated sulphuric acid leads to polymerisation, sulphona-tion, etc., so that the original component cannot be recovered unchanged this solvent, therefore, possesses hmited apphcation. Phenols may be separated from acids (for example, o-cresol from benzoic acid) by a dilute solution of sodium bicarbonate the weakly acidic phenols (and also enols) are not converted into salts by this reagent and may be removed by ether extraction or by other means the acids pass into solution as the sodium salts and may be recovered after acidification. Aldehydes, e.g., benzaldehyde, may be separated from liquid hydrocarbons and other neutral, water-insoluble hquid compounds by shaking with a solution of sodium bisulphite the aldehyde forms a sohd bisulphite compound, which may be filtered off and decomposed with dilute acid or with sodium bicarbonate solution in order to recover the aldehyde. 

If the water insoluble mixture is a liquid, evaporate a small sample (say, 4 ml.) in an evaporating dish on a water bath in order to determine the amount of volatile components, if any. If the solvent distils at the temperature of the boihng water bath, it is advisable to distil ofiF this solvent on a water bath and to replace it by ether. 

The above procedure for water-insoluble mixtures is shown, in outline, in tabular form in Table XI,9,1. If the mixture is a liquid, the volatile solvent is assumed to have been removed. 

TABLE XI,9,1. GENERAL SCHEME FOR SEPARATION OF A WATER-INSOLUBLE MIXTURE... 

Ether solution. Contains water- insoluble amines. Aqueous solution. Will possess ammo, niacal odour of water-soluble amines present. Distil as long as distillate is alkaline to recover volatile water-soluble amines. 

The fourth and most interesting of the polymerization techniques we shall consider is called emulsion polymerization. It is important to distinguish between suspension and emulsion polymerization, since there is a superficial resemblance between the two and their terminology has potential for confusion A suspension of oil drops in water is called an emulsion. Water-insoluble monomers are used in the emulsion process also, and the polymerization is carried out in the presence of water however, the following significant differences also exist ... 

Superabsorbents. Water-sweUable polymers are used extensively in consumer articles and for industrial appUcations. Most of these polymers are cross-linked acryUc copolymers of metal salts of acryUc acid and acrylamide or other monomers such as 2-acrylamido-2-methylpropanesulfonic acid. These hydrogel forming systems can have high gel strength as measured by the shear modulus (134). Sometimes inorganic water-insoluble powder is blended with the polymer to increase gel strength (135). Patents describe processes for making cross-linked polyurethane foams which contain superabsorbent polymers (136,137). 

Emulsion Process. The emulsion polymerization process utilizes water as a continuous phase with the reactants suspended as microscopic particles. This low viscosity system allows facile mixing and heat transfer for control purposes. An emulsifier is generally employed to stabilize the water insoluble monomers and other reactants, and to prevent reactor fouling. With SAN the system is composed of water, monomers, chain-transfer agents for molecular weight control, emulsifiers, and initiators. Both batch and semibatch processes are employed. Copolymerization is normally carried out at 60 to 100°C to conversions of - 97%. Lower temperature polymerization can be achieved with redox-initiator systems (51). 

Gum tragacanth is obtained from the large tap root and branches of a small perennial shmb found in the Middle East, especially Iran. Chemically, it is a mixture of water-insoluble polysaccharides. It is stable to heat, acidity, and aging, and is used extensively in pourable low calorie salad dressings. 

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