Sodium hydroxide equivalent mass

To a solution of 4.76 g of 1-(4 -methyl-6 -methoxy-2 -pyrimidinyl)-3-methyl-3-pyrazoline-5-one in 200 ml of ether was added an ether solution containing 6 molar equivalents of diazomethane and the reaction mixture was allowed to stand at room temperature for 20 hours. After distilling off the solvent, the residue was dissolved in 160 ml of water, made alkaline (pH 10) with sodium hydroxide solution and extracted three times with 140 ml of benzene. The extract was washed with a small amount of water, dried over sodium sulfate and evaporated to give a crystalline mass. Recrystallization from isopropylether gave 1-(4 -methyl-6 -methoxy-2 -pyrimidinyl)-3-methyl-5-methoxypyrazole (3.96 g, 84%) as colorless prisms, MP 90° to 92°C. 

The equivalent of a base is that mass of it which contains one replaceable hydroxyl group, i.e. 17.008 g of ionisable hydroxyl 17.008 g of hydroxyl are equivalent to 1.008 g of hydrogen. The equivalents of sodium hydroxide and potassium hydroxide are the mole, of calcium hydroxide, strontium hydroxide, and barium hydroxide half a mole. 

Take the two reactions of phosphoric acid with sodium hydroxide that follow. These reactions will illustrate that the equivalent mass of a given substance depends upon the chemical reaction in which the substance is involved. 

Three molar equivalents of bromine is added with cooling to a mixture of 1 molar equivalent of quinoline and 3 gram-atom equivalents of sulfur, and the resulting mixture is heated to 180-200" in an oil bath for 2 hours. The cooled reaction mass is extracted several times with hot concentrated hydrochloric acid, and the combined extracts are made alkaline with sodium hydroxide. Ether extraction of the alkaline mixture followed by distillation of the ethereal solution gives a 50% yield of 3-bromoquinoline boiling at 158—162°/24 mm. 

Mercury bis-a-acetyl-a-isopropyl or Mercury-bis-aceto-di-methyl-methane, [CHgCO.CMeg—JgHg.—Mercuric dimethyl aceto-acetate is heated in a vacuum at 90 C., when it is found to lose two molecular equivalents of carbon dioxide, which is shown by the loss in weight. The resulting mass is extracted with acetone, and the solvent removed m vacuo, the product isolated melting at 120 C. It is soluble in acetone, alcohol, toluene, or xylene, but only slightly soluble in ether. Mercuric sulphide is split off from it by the action of ammonium sulphide, but no mercuric oxide is formed when sodium hydroxide is added. The compound soon decomposes with the deposition of metallic mercury. 

If the unknown substance is a carboxylic acid, it may be titrated with a standardized solution of sodium hydroxide. By use of this procedure, a neutralization equivalent can be determined. The neutralization equivalent is identical to the equivalent weight of the acid. If the acid has only one carboxyl group, the neutralization equivalent and the molecular mass are identical. If the acid has more than one carboxyl group, the neutralization equivalent is equal to the molecular mass of the acid divided by the number of carboxyl groups. Many phenols, especially those substituted by electron-withdrawing groups, are sufficiently acidic to be titrated by this same method, as are sulfonic acids. 

The acidity of carboxylic acids enables ready determination of the equivalent mass or neutralization equivalent of the acid by titration with standard base. The equivalent weight of an acid is that mass, in grams, of acid that reacts with one equivalent of base. As an example, suppose that 0.1000 g of an unknown acid requires 16.90 mL of 0.1000 N sodium hydroxide solution to be titrated to a phenolph-thalein endpoint. This means that 0.1000 g of the acid corresponds to (16.90 mL) (0.1000 equivalent/1000 mL) or 0.0016901 equivalent of the acid, or that one equivalent of the acid weighs 0.1000/0.00169 or 59.201 g. Thus the following expression applies ... 

Free fatty acids can be efficiently extracted with acidified mixture of hexane/ tert-butyl methyl ether. Acids, esters, and salts are saponified with sodium hydroxide and esterified (transesterified) with methanol. Methyl esters are conveniently separated and determined by gas chromatography with a flame-ionization detector. Combination of gas chromatography and mass spectrometry, GC-MS, is one of the methods of choice for analysis of methylated fatty acids. Equivalent chain length of fatty acid can be calculated from the retention time. 

Crude oils may be up to 15% FFA, while refined oils will be <0.1%. Measurement of FFA is normally done by titration of an ether-ethanol solution of the fat with standardized aqueous sodium or potassium hydroxide, in the presence of phenolphthalein indicator (see ISO 660 1983). This method is very accurate, using the molecular weight of oleic acid (282) for all calculations. Accuracy is improved by using the average molecular mass of the fatty acids in the fat, calculated from the FA composition (e.g., for palm oil 256 is used, for palm kernel/coconut oil 200 is used). The results are expressed either as acid value the number of milligrams of potassium hydroxide required to neutralize 1 g of the fat, or, FFA% the percentage concentration of oleic acid equivalent to the free acids present. 

---