Hydrogen melting point

Crystallise the two lots of crude active aec. -octyl hydrogen phthalates separately twice from 90 per cent, acetic acid use 2 g. of acetic acid to each gram of soUd. The recrystaUised esters, if optically pure (8), will melt sharply at 75° if the melting points are below 75°, further recrystallisation is necessary. The yields of optically pure products, m.p. 75°, are 48 g. and 49 g. respectively. 

The derivative selected in any particular instance should be one which clearly singles out one compound from among all the possibilities and thus enables an unequivocal choice to be made. The melting points of the derivatives to be compared should differ by at least 5-10°. Whenever possible, a derivative should be selected which has a neutralisation equivalent as well as a melting point (e.g., an aryloxyacetic acid derivative of a phenol. Section IV,114,4, or a hydrogen S nitrophthalate of an alcohol. Section 111,25,5). 

Liquid hydrogen is important in cryogenics and in the study of superconductivity, as its melting point is only 20 degrees above absolute zero. 

Hydrogen bonding m carboxylic acids raises their melting points and boiling points above those of comparably constituted alkanes alcohols aldehydes and ketones... 

Barium fluoride [7782-32-8] Bap2, is a white crystal or powder. Under the microscope crystals may be clear and colorless. Reported melting points vary from 1290 (1) to 1355°C (2), including values of 1301 (3) and 1353°C (4). Differences may result from impurities, reaction with containers, or inaccurate temperature measurements. The heat of fusion is 28 kj/mol (6.8 kcal/mol) (5), the boiling point 2260°C (6), and the density 4.9 g/cm. The solubiUty in water is about 1.6 g/L at 25°C and 5.6 g/100 g (7) in anhydrous hydrogen fluoride. Several preparations for barium fluoride have been reported (8—10). 

The location of the hydroxyl and aldehyde groups ortho to one another in saUcylaldehyde permits intramolecular hydrogen bonding, and this results in the lower melting point and boiling point and the higher acid dissociation constant observed relative to -hydroxybenzaldehyde. 

Rea.ctlons, When free (R-R, R -tartaric acid (4) is heated above its melting point, amorphous anhydrides are formed which, on boiling with water, regenerate the acid. Further heating causes simultaneous formation of pymvic acid, CH COCOOH pyrotartaric acid, HOOCCH2CH(CH2)COOH and, finally, a black, charred residue. In the presence of a ferrous salt and hydrogen peroxide, dihydroxymaleic acid [526-84-1] (7) is formed. Nitrating the acid yields a dinitro ester which, on hydrolysis, is converted to dihydroxytartaric acid [617 8-1] (8), which upon further oxidation yields tartronic acid [80-69-3] (9). 

Reduction to Solid Metal. Metals having very high melting points caimot be reduced in the Hquid state. Because the separation of a soHd metallic product from a residue is usually difficult, the raw material must be purified before reduction. Tungsten and molybdenum, for instance, are prepared by reduction of a purified oxide (WO, MoO ) or a salt, eg, (NH2 2 G4, using hydrogen. A reaction such as... 

Table 4. Melting Points of Some Peroxy Compounds from Aldehydes and Hydrogen Peroxide ...

Phosphonic Acid and P(III) Derivatives. Phosphonic or phosphorous acid is a white dehquescent crystalline compound having a melting point of 73.6°C. As evidenced by its stmcture,HP(=0)(0H)2, phosphonic acid is dibasic. The first hydrogen is strongly ionized, pR 1.3—1.7, and... 

Some time earlier, Eastman-Kodak has been working on a novel polyester as an entry into the important polyester fiber market and had devised a new ahcychc diol, 1,4-cydohexanedimethanol [105-08-5] effectively made by exhaustive hydrogenation of dimethyl terephthalate. Reaction of the new diol with dimethyl terephthalate gave a crystalline polyester with a higher melting point than PET and it was introduced in the United States in 1954 as a new polyester fiber under the trade name Kodel (5). Much later the same polyester, now called PCT, and a cyclohexanedimethanol—terephthalate/isophthalate copolymer were introduced as mol ding resins and thermoforming materials (6). More recentiy stiU, copolymers of PET with CHDM units have been introduced for blow molded bottie resins (7). 

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