Precipitation equivalent weights

Materials. Reagent grade solvents, dimethyl formamide (DMF), dimethyl acetamide (DMAC), dimethyl sulfoxide (DMSO) and methanol were purchased from Baker, stored over molecular sieves once opened, and used without further purification. Aminoethane thiosulfuric acid (AETSA) purchased from Kodak, and Taurine, purchased from Alfa were purified by recrystallization. Each was thrice recrystallized from hot, deionized water. The crystalline precipitate was dried (48 hours at 40 °C) in-vacuo and subsequently stored in a desiccator. Benzophenone (BP) was purchased from Aldrich Chemical Company. QUANTACURE BTC (BTC), (4-benzolybenzyl) trimethylammonium chloride, was used as supplied by Aceto, Inc., Flushing, New York. Phenyl glycidyl ether (PGE) was purchased from MCB, distilled in-vacuo. and stored at -15 °C. Epon 828 was used as supplied bv Shell Chemical Company. The epoxy equivalent weight (EEW) for Epon 828 determined by an appropriate titration, was found to be 187.7. 

The salt was dissolved in 300 ml water, and insoluble matter was removed from the solution by filtration. The free acid was precipitated from the filtrate at 50°C to 60°C by the addition of 40 ml 1 1 hydrochloric acid. The precipitate was filtered off after a few hours, washed with water, and dried. There were obtained 34 g 3-acetylaminomethyl-5-acetylamino-2,4,6-triiodobenzoic acid (79% of theoretical yield) having a melting point of 246°C to 248°C. The equivalent weight of this practically pure acid was found to be 631 as compared to the calculated value of 627.96. 

Only rarety is the sulfate of the nitrated base so insoluble that it separates directly on dilution of the reaction mixture as in the above example. In many cases, the hydrochloride can be precipitated by the addition of salt. Frequently, however, it is necessary to neutralize the entire amount of sulfuric acid in order to isolate the product, but this cannot be done with lime because then calcium sulfate would be precipitated with the base. In industrial preparations, tlie neutralization is done with magnesia, of which only a small amount is required because of its low equivalent weight, or with ammonia. In the latter case, the filtrate is treated with lime and the ammonia is recovered and used again. It is preferable to cany out the neutralization in steps, because most of the impurities are precipitated mst, and the later fractions are pure. 

Vacuum-still bottoms from the H-coal liquefaction process were separated into acid, neutral, and basic fractions by precipitation with acids or by extraction with bases. About one-third of the preasphaltene and one-sixth of the asphaltene fraction were precipitated by acids equivalent weights of the bases were in the range 1200-1800 for preasphaltenes and 600-800 for asphaltenes. The acidic components were obtained either by extraction with aqueous sodium hydroxide or by extraction with benzyltrimethylammonium hydroxide in methanol. About one-fifth of the asphaltene and one-fourth of the presasphaltene fractions were obtained as acids, and up to 10% as amphoteric substances. Nitrogen and sulfur were present in all fractions found. Deno axidation (CF3C02H, H202, H 04) gave dicarboxylic acids from malonic to adipic in addition to mono acids. 

Equivalent Weights. The equivalent weights of the salts precipitated from toluene solution were determined by titration with sodium hydroxide. Some difficulty was encountered in finding a suitable solvent for the titrations, but two methods were developed for obtaining reproducible titration results. 

The phosphotungstate salts cannot be used for equivalent weight determinations, for their characteristically variable composition leads to inconsistent titration results. However, treatment of the salts with aqueous sodium hydroxide led to recovery of the free bases in reproducible amounts. These results show that one-fifth of the high molecular weight asphaltenes and one-third of the preasphaltenes are precipitated as phosphotungstate salts. Considerably less of the unfractionated H-coal vacuum-still bottoms and none of the low molecular weight asphaltenes and oils and resins were separated in this manner. 

Equivalent Weights in Precipitation and Complex Formation Reactions... 

The equivalent weight of a participant in a precipitation or a complex formation reaction is that weight which reacts with or provides one mole of the reacting cation if it is univalent, one-half mole if it is divalent, one-third mole if it is triva-lent, and so on. It is important to note that the cation referred to in this definition is always the cation directly involved in the analytical reaction and not necessarily the cation contained in the compound whose equivalent weight is being defined. 

Define equivalent weights for AICI3 and BiOCl if the two compounds are determined by a precipitation titration with AgN03 ... 

Where surfactants were used in these experiments they were present in relatively large concentration. Hill and Lake, for example, injected a solution containing 0.046 meq/ml of a surfactant mixture having an average equivalent weight of 410 thus, the surfactant concentration was about 1.9 wt.%. Since this concentration is far above the CMC for the surfactants involved, multivalent cations may be bound by the micelles with the result that calcium sulfonate precipitation does not occur. 

The calcium tolerance of a selected group of crude alkylbenzene sulfonates is summarized in Table II. These results, while relatively imprecise, indicate that the calcium tolerance of these surfactants in dilute solutions is quite low. In general, the calcium tolerance decreases as the equivalent weight increases, and the addition of 3 wt.% n-butanol or 2-butanol does not appear to improve stability. Finally, the onset of precipitation does not appear to be very sensitive to temperature. 

If appreciable precipitation occurs, however, it leads to erroneous adsorption data—as we have noted in several cases. The problem is obviously more serious with the higher equivalent weight surfactants (Eq. wt. > 400) and these are the surfactants of greatest interest for improved oil recovery by micellar flooding. 

Salting-out of alkylbenzene sulfonates from relatively dilute solutions by NaCl has been found to be substantial if the alkyl chain contains more than about 12 carbons. Similarly, the multivalent cation tolerance of alkylbenzene sulfonates in dilute solutions has been found to be small and strongly dependent on equivalent weight. In general, if the equivalent weight exceeds 350 (alkyl chain more than 12 carbons), the calcium tolerance appears to be extremely small. The addition of short-chain alcohols appears to be of limited benefit in preventing either salt-ing-out by NaCl or multivalent cation precipitation. 

One mole of Fe or Fe reacts or is produced per mole of electrons so that the equivalent weights of each of these species are the same as the molecular weights. Note that if Fe + and Fe were to participate in a precipitation-dissolution reaction, the equivalent weights would be one half and one third of the molecular weights, respectively. 

Cesium chloride [7647-17-8] M 168.4, m 645°, b 1303°, d 4 3.99. It is soluble in H2O but can be purified by crystallisation from H2O [solubility in g percent 162.3(0.7°), 182.2(16.2°) and 290(at bp 119.4 )] and dried in a high vacuum. It is soluble in EtOH and is deliquescent, keep it in a tightly closed container. [Donges in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 951-955 1963.] For further purification of CsCl, a concentrated aqueous solution of the practically piue reagent is treated with an equivalent weight of I2 and CI2 is bubbled into the solution until precipitation of CsCy is complete. Recrystallisation yields a salt that is free from other alkali metals. It is then decomposed to pure CsCl on heat-... 

---