Water-insoluble salts, preparation

Water-soluble salts are best purified by preparing a concentrated aqueous solution to which, after decolorising with charcoal and filtering, ethanol or acetone is added so that the salts crystallise. They are collected, washed with aqueous ethanol or aqueous acetone, and dried. In some cases, water-soluble salts can be recrystallised satisfactorily from alcohols. Water-insoluble salts are purified by Soxhlet extraction, first with organic solvents and then with water, to remove soluble contaminants. The purified salt is recovered from the thimble. 

If the solubility of a drug is to be reduced to enhance stability or to prepare a suspension, the for-mulator may prepare water-insoluble salts. A classic example is procaine penicillin G, the decreased solubility (7 mg/mL) of which, when compared with the very soluble penicillin G potassium, is utilized to prepare stable parenteral suspensions. Another alternative to preparing an insoluble drug is to use the parent acidic or basic drug and to buffer the pH of the suspension in the range of minimum solubility. 

Water-insoluble salts may also be prepared using ion-exchange resins. Metal drug salts, in contrast to organic salts, may be problematic with respect to taste because of their alkalinity. Salts incorporating the sweet-tasting A-cyclohexylsulfamic acid (cyclamate) as the counterion can render bitter drugs such as dextromethorphan and chlorpheniramine palatable. ... 

In the initial approach, and before the action of acidic excipients was clearly understood, the slightly acidic and relatively water insoluble salt, calcium lactate, was used with the hopes of catalyzing long term surface erosion of linear poly (ortho esters). In this work, rod-shaped devices were prepared by incorporating 30 wt% levonorgestrei and 2 wt% calcium lactate into a polymer prepared from 3,9-bis (ethylidene-2,4,8,10-tetraoxaspiro [5,5] undecane) and a 60/40 mol mixture of trans-cyclohexane dimethanol and 1,6-hexanediol and the devices were implanted into rabbits. The devices were then explanted at various time intervals and examined by scanning electron microscopy. A device ex-planted after 10 weeks is shown in Fig. 27 [25]. 

Water-Insoluble Salts. Many important salts for 7r-complexation are water-insoluble. The best examples are cuprous (Cu+) salts, e.g., CuCl. The most practical technique for preparing monolayer CuCl is by a two-step process incipient wetness impregnation of CuCE followed by reduction to CuCl. This process also applies to other cuprous salts, as the cupric salts are generally water-soluble. Attempts have also been made for direct impregnation of CuCl. This could be accomplished by two ways using acid or basic solutions or dissolving CuCl with the aid of ammonium chloride. These two techniques will be first briefly described, and the two-step process will be then discussed in more details. 

Ce(III) forms a water-insoluble hydroxide, carbonate, oxalate, phosphate, and fluoride sparingly soluble sulfate and acetate and soluble nitrate and chloride (and bromide). In solution the salts are only slightly hydrolyzed. The carbonate is readily prepared and is a convenient precursor for the preparation of other derivatives. The sparingly soluble sulfate and acetate decrease in solubihty with an increase in temperature. Calcination of most Ce(III) salts results in Ce02. 

Hydrochloric acid and sulphuric acid are widely employed in the preparation of standard solutions of acids. Both of these are commercially available as concentrated solutions concentrated hydrochloric acid is about 10.5- 12M, and concentrated sulphuric acid is about 18M. By suitable dilution, solutions of any desired approximate concentration may be readily prepared. Hydrochloric acid is generally preferred, since most chlorides are soluble in water. Sulphuric acid forms insoluble salts with calcium and barium hydroxides for titration of hot liquids or for determinations which require boiling for some time with excess of acid, standard sulphuric acid is, however, preferable. Nitric acid is rarely employed, because it almost invariably contains a little nitrous acid, which has a destructive action upon many indicators. 

Far less than the stoichiometric amount of sequestrants precipitation of insoluble salts from water hardness can be prevented by slowing down the formation of crystals and crystal growth. This process is called the threshold effect. It has long been used in the preparation of boiler feeding water, e.g., steam vessels of railroad engines. Originally sodium pyrophosphate was used for this task, but alkylphosphonic acids and derivatives thereof are superior in their effect. 

EGS is water-insoluble and must be dissolved in an organic solvent prior to its addition to an aqueous reaction. Prepare a concentrated solution of EGS in DMF or DMSO and add an aliquot of the stock solution to the reaction. Do not exceed a concentration of more than about 10 percent organic solvent in the aqueous reaction buffer or precipitation of buffer salts or protein may occur. 

Many attempts to alter the physical properties of neomycin by the formation of various salts have been described. Thus the neomycin salts of the higher fatty acids, such as the stearate, palmitate and myristate3(3 31 were prepared and being water-insoluble were formulated in ointment bases. Similarly, the undecylenate salt has been prepared and processes for its production patented3 33 34 The undecylenate and caprylate salts have been described as being particularly suitable as antimitotic compounds35. 

Sodium alginate forms a raft on the stomach contents leading to a reduction in reflux. Aluminium is an insoluble salt that is used as an antacid with no particular advantage in reflux. Chloroform water is a traditional preparation to reduce colic. Sucrose and lactose are sugars with no effect on gastro-oesophageal reflux disease. 

The physical and chemical properties of elemental thorium and a few representative water soluble and insoluble thorium compounds are presented in Table 3-2. Water soluble thorium compounds include the chloride, fluoride, nitrate, and sulfate salts (Weast 1983). These compounds dissolve fairly readily in water. Soluble thorium compounds, as a class, have greater bioavailability than the insoluble thorium compounds. Water insoluble thorium compounds include the dioxide, carbonate, hydroxide, oxalate, and phosphate salts. Thorium carbonate is soluble in concentrated sodium carbonate (Weast 1983). Thorium metal and several of its compounds are commercially available. No general specifications for commercially prepared thorium metal or compounds have been established. Manufacturers prepare thorium products according to contractual specifications (Hedrick 1985). 

Tetraquo-diammino-chromic Chloride, [Cr(NH8)2(H2Q)4]Cl3, is prepared in the same manner as the bromide by decomposing the basic salt. It forms light red monoclinic prisms which are very soluble in water, insoluble in alcohol, and on warming the aqueous solution with a little acid is transformed into the dichloro-diaquo-salt. 

Determining the Solubility of Potassium Dichromate. Prepare a potassium dichromate solution that is saturated at room temperature. Using the table of solubility (see Appendix 1, Table 1), calculate the amount of potassium dichromate needed for the saturation of 50 ml of distilled water, and take an excess of it (10%). Place the amount of salt weighed on a technical chemical balance in a 100-ml flask and add 50 ml of distilled water to it. Close the flask with a stopper and stir its contents during 10-15 min (better in a shaker) while holding the flask by its neck. Prior to filtration, measure the temperature of the solution. Filter off the remaining insoluble salt and gather the filtrate in a dry flask. 

Indium orthophosphate is essentially insoluble in water, but salts of [In(P04)2]3- and [In2(P04)4]6- have been prepared,163 and a solution phase complex with the H2POj anion has been identified.164 The coordination chemistry of In3+ with the higher phosphates is at present ill defined. Stability constant measurements,9 and preparative and spectroscopic studies7 suggest that In06 is the central core of the compounds in the solid state. The same appears to be true for the complexes reported for L = fluorophosphate,165 methylphosphonate,166 dichlorophosphate,167 dimethylthiophosphate,168 diethylthiophosphinate169,170 and diisopropyl-methylphosphonate.171... 

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