Sulphuric acid dehydrating value

Reaction XXIX. (a) Condensation of a Phenol with Phthalic Anhydride to form a Phthalein. (A., 183, 1 202, 68.)—The phthaleins result from the condensation of phthalic anhydride (1 mol.) with phenols (2 mols.) on heating with dehydrating agents—sulphuric acid, fused zinc chloride (to 120°) or anhydrous oxalic acid (to 115°). These compounds are particularly important some are dyes of great technical value. The simplest representative of the class is phenolphthalein. 

First value input of sulphur section second value after initial dehydration of aqueous sulphuric acid. 

The pXr values of diarylmethyl cations [22C ] were basically those determined according to the same method as for the triarylmethyl cations in aqueous sulphuric acid solutions by Deno and coworkers (Deno et ai, 1955 Deno and Schriesheim, 1955 Deno and Evans, 1957). For reasons of solubility, a wide set of pXr+ values in aqueous acetic acid solutions were determined by Mindl and coworkers (Mindl and Vecera, 1971, 1972 Mindl, 1972). Unfortunately, however, the pXr+ values, determined by means of the protonation-dehydration method for diarylmethanols, could only be obtained for more stable derivatives and not for those less stable than the unsubstituted... 

This apparatus has the form shown in Fig. 161. It consists of a U-tube, the limbs of which are bent close together, and placed in front of a millimetre scale. The bend of the tube is filled with oil or other suitable liquid, e.g. bromonaphthalene. If it is desired to measure the dissociation pressure of, say, a salt hydrate, concentrated sulphuric acid is placed in the flask e, and a quantity of the hydrate, well dried and powdered, in the bulb d. The necks of the bulbs d and e ai e then sealed off. Since, as we have learned, suspended transformation may occur, it is advisable first partially to dehydrate the salt, in order to ensure the presence of the second solid product of dissociation the value of the dissociation pressure being independent of the degree of dissociation of the hydrate (p. 81). The small bulbs d and e having been filled, the apparatus is placed on its side, so as to allow the liquid to run from the bend of the tube into the bulbs a and b it is then exhausted through / by means of a mercury pump, and sealed off. 

Recently, we have elaborated an alternative method of the drimenol (2) synthesis from the hydroxy ketone (63) of preparative value [49]. In the article [46] it was shown that on oxidation of the hydroxy ketone (63) with trifluoroperacetic acid under certain conditions, the 11-monoacetate of drimane-8a,l 1-diol (42) is obtained in the quantitative yield. On treatment of the compound (42) at room temperature with 30% solution of concentrated sulphuric acid in ethanol by using 10 ml of this solution per 1 g of the compound (42), the crystalline drimenol (2) was obtained in 56% yield, which could be purified by recrystallisation from n-hexane [49] (Scheme 10). In such a way, at stage e) selective dehydration and transesterification of the hydroxy acetate (42) took place. 

The heat of solution of NiBr2 in water was reported as - (82.09 + 0.17) kJ-mol based on limited measurements and analysis. The solid was obtained by dehydration over sulphuric acid in a vacuum desiccator, and the Ni and Br analyses were within 0.2% of theoretical. The number of samples measured was not reported, but some values in the same paper were based on only two measurements. Neither the dilution of the final solution nor the sample size was given. The enthalpy value probably was not corrected for dilution, as there is no description of a correction procedure. The uncertainty reported was probably lo. The resulting value is approximately 4 kJ-mol less exothermic than that of Efimov and Furkalyuk [90EF1/FUR] (although the final solutions probably were somewhat different). 

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