The thermal behaviour of D-mannitol, dulcitol, D-sorbitol, the semihydrate of D-sorbitol, L-arabitol, xylitol and ribitol was investigated by means of differential thermal analysis and a derivatograph. AII these polyols are stable up to 200--250 ~ The endothermic peaks on the DTA curves at lower temperatures are due to melting. These effects are not accompanied by an increase in the electric conductivity. The hexitols decompose endothermally at boiling above 200--250 ~ the majority of the decomposition products boil out, and the residue is oxidized. The beginning of the decomposition of the pentitols is accompanied by an exothermic peak.
The possibility of detecting the direction of reaction of boric acid with polyol and its intermediate stages by means of the data obtained with a Derivatograph is shown.
Thermal decomposition of iron(II) and cobalt(II) hexaborates has been investigated. The methods applied to investigate the process were differential thermal analysis, derivatography, crystallooptics and x-ray study. The following iron(II) hexaborate hydrates, FeO 9 3B~O 3 9 7.5H20, FeO " 3B203 9 5H20, FeO 9 3B~O, 9 0.5H~O; iron(III) borates, FelOn" 6B~O3 and 2Fe208 "B20~; cobalt(II)hexaborate hydrates CoO 9 3B20~ 9 7.5H~O, CoO 9 3B~O3 9 5H20, CoO 9 3B.zO 8 9 0.SHOO, CoO 9 3B~Oz and the decomposition product 2CoO 9 3B~Oz have been isolated. Hepta-and semihydrates of cobalt(II) and iron(II) hexaborates have been proved to be isomorphous. It has been established that in the case of cobalt and iron hexaborates the exothermic maximum refers to a decomposition reaction and to the formation of a borate containing a smaller proportion of boron and boric anhydride.In the present paper the thermal decomposition of iron(II) and cobalt(II) hexaborates is described. Intermediates and final products of thermal decomposition were isolated and identified by means of chemical analysis, optical study of crystals, and by taking the corresponding debayegrams (Fe-radiation). Thermogravimetric (TG) and derivative thermogravimetric (DTG) curves were taken by means of the F. Paulik, J. Paulik, L. Erdey Derivatograph [1] using 0.1-0.2 g samples at a heating rate of 12 ~ per minute. Differential thermal analysis (DTA) and electrical conductivity (TE)curves were taken by an FPK-59 apparatus simultaneously at the same rate of heating [2]. TG, DTG, DTA and TE curves are presented in common figures (Figs 1 and 2). Optical indexes of crystals were determined by means of the immersion method.Iron(II) and cobalt(II) hexaborates were synthesized according to methods given in references [3,4]; their analysis was carried out as follows: BzO 3 was determined according to [5], CoO complexometrically, Fe(II) by titration with potassium permanganate, and Fe(III) by reduction with ascorbic acid, the excess of the latter being titrated iodometrically. The water of crystallization was determined volumetrically by means of lithium hydride [6] using L. Berg's automatic burette. By stopping the heating of the sample in the derivatograph furnace at temperatures where the separate dehydration stages ended, intermediate hydrates were isolated. Likewise the intermediates of decomposition formed directly before as well as after the "borate regrouping" were also isolated. The properties 2
Thermal analysis shows that the interaction of boric acid with pentaerythritol on heating leads to the formation of a polymeric complex acid (1 : 1) and the direction of the interaction does not depend on the molar ratio of the reacting compounds. The interaction of boric acad with methriol and ethriol leads to the formation of two types of esters, depending on the molar ratio of the reactants. The formation of an unstable polyolboric acid is an intermediate stage of each interaction.
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