Crystalline salts melting point

The first step involves analyzing solid salts for crystallinity and melting point. Crystalline salts are usually the most desirable, because they exhibit superior processing, handling, stability, and purification properties. Low-melting salts may be relegated to a lower-priority status at this point. 

Drop 1 g. of sodium into 10 ml. of ethyl alcohol in a small flask provided with a small water condenser heat the mixture until all the sodium has dissolved. Cool, and add 1 g. of the ester and 0-5 ml. of water. Frequently the sodium salt of the acid will be deposited either at once or after boiling for a few minutes. If this occurs, filter oflF the solid at once, wash it with a little absolute ethyl alcohol (or absolute methylated spirit), and convert it into the p-bromophenacyl ester, p-nitro-benzyl ester or S-benzyl-tso-thiuronium salt (for experimental details, see Section 111,85). If no solid separates, continue the boiling for 30-60 minutes, boil oflF the alcohol, allow to cool, render the product just neutral to phenolphthalein with dilute sulphuric or hydrochloric acid, convert the sodium salt present in solution into a crystalline derivative (Section 111,85), and determine its melting point. 

Sulphonic acids. The aromatic sulphonic acids and their alkali metal salts are soluble in water, but insoluble in ether (Solubility Group II). They are best characterised by conversion into crystalline S-benzyl-iso-thiuronium salts (see Section IV,33,2 and 111,85,5), which possess characteristic melting points. A more time-consuming procedure is to treat the well-dried acid or... 

The normal salt, CH COONH, is a white, deUquescent, crystalline soHd, formula wt 77.08, having a specific gravity of 1.073. It is quite soluble in water or ethanol 148 g dissolve in 100 g of water at 4°C. The salt s solubiUty in water increases only slightly as temperature increases up to about 25 °C. The specific gravity of aqueous neutral ammonium acetate ranges from 1.022 to 1.092 as solution concentration increases from 10 to 50 wt % (4). The normal salt melts at 114°C, but decomposes before reaching its boiling point. 

Strontium carbonate is a colorless or white crystalline soHd having a rhombic stmcture below 926°C and a hexagonal stmcture above this temperature. It has a specific gravity of 3.70, a melting point of 1497°C at 6 MPa (60 atm), and it decomposes to the oxide on heating at 1340°C. It is insoluble in water but reacts with acids, and is soluble in solutions of ammonium salts. 

Cesium perchlorate [13454-84-7], CsClO, mol wt 232.35 and theoretical cesium content hi.25/q, is a crystalline powder that decomposes at 250°C Cesium fluoride [13400-13-0], CsF, mol wt 151.90, theoretical cesium content 87.49%, has a melting point of 682—703°C and a boiling point of 1253°C. Cesium fluoride is an extremely hygroscopic, colorless, crystalline soUd it has a solubUity of 3.665 kg/L of water at 18°C. Cesium fluoride is made by exactly neutrali2ing cesium hydroxide with hydrofluoric acid and evaporating the resultant solution to dryness at 400°C. Excess HE results in a bifluoride salt that does not decompose at 400°C, and carbonate in the starting material gives an alkaline product. 

The purity of (/-a-phenylethylamine-/-malate is not readily determined by its melting point or specific rotation, but rather by its massive crystalline form and solubility. The acid and neutral /-base-/-acid salts are much more soluble, and usually do not crystallize at all. 

Melamine, a non-hygroscopic, white crystalline solid, melts with decomposition above 347°C and sublimes at temperatures below the melting point. It is only slightly soluble in water 100 ml of water dissolve 0.38 g at 20°C and 3.7 g at 90°C. It is weakly basic and forms well-defined salts with acids. 

The acetyl group in aconitine may be eliminated in two other ways (a) by heating aconitine in sealed tubes with methyl alcohol, when methylbenzoylaconine, m.p. 210-1°, is formed, or (b) by heating the alkaloid at its melting-point, when pyraconitine, C32H43O9N, m.p. 167-5° (171°, Schulze), [a] ° — 112-2° (EtOH), is formed. The latter yields crystalline, laevorotatory salts, and on hydrolysis by alkalis affords benzoic acid and pyraconine, C2sH3gOgN, amorphous, [a]n — 91° (HgO), but yields a crystalline hydrochloride, B. HCl. 2-5H20, m.p. 154° (135°, Schulze), Md - 102° (HgO) (- 124-6°, Schulze). ... 

On evaporation of the ethyl ether from the ethyl ether solution, the benzhydryl ether was recovered as a pale yellow oil. The benzhydryl ether was dissolved in 60 ml of isopropanol and the isopropanol solution acidified to a pH of 3 with dry hydrogen chloride-methanol solution. The acidic propanol solution was then diluted with ethyl ether until a faint turbidity was observed. In a short time, the crystalline hydrochloride salt of the benzhydryl ether separated from the propanol solution. The crystallized salt was recrystallized once from 75 ml of isopropanol with the aid of ethyl ether in order to further purify the material. A yield of the pure hydrochloride salt of 1-methylpiperidyl-4-benzhydryl ether of 24.5 grams was obtained. This was 39% of the theoretical yield. The pure material had a melting point of 206°C. 

The crude product separates as a solid from the reaction medium and is recovered by filtration, and it is then washed thoroughly with ether and dissolved in 350 ml 1 N HCI. Then, approximately 250 ml of the aqueous solvent is removed with a rotary evaporator and the evaporation residue combined with 125 ml methanol and filtered through decolorizing charcoal. The product is precipitated as the HCI salt by the addition of 7 parts of acetone. The resulting crystalline material is removed by filtration dried at 40°C with vacuum, and has a melting point of about 242°C and Is used without further purification. 

The crude iodinated acid was then dissolved in 500 ml of 95% alcohol, 10 g of dimethyl-aminoethanol was added, the solution was decolorized with activated charcoal and filtered at 70°C. After keeping the filtrate for several hours at 5°C, the heavy crystalline precipitate which formed was collected by filtration and washed with acetone. The mother liquors were concentrated to 150 ml and cooled to give a second crop which was further purified by recrystallization from 50 ml of 95% alcohol. In this way a total of 36.0 g of dimethyl-aminoethanol salt of dextro-/3-(3,5-diiodo-4-hydroxy)-o-phenylpropionic acid, MP 151° to 153°C, was obtained. The melting point of the dimethylaminoethanol salt of unresolved /3-(3,5-diiodo-4-hydroxy)-o-phenylpropionic acid was 142° to 144°C. 

Upon the addition of ethanolic HCI to a solution, cooled to 0°C, of 26.38 parts of the free base in 130 parts by volume of absolute ethanol, until a Congo-acid reaction is achieved, the crystalline dihydrochloride of 3-ethylmercapto-10-[3 -(1 "-methyl-piperazyl-4")-propyl-1 ] -phenothiazine is precipitated. The analytically pure salt has a melting point of 214°C to 216°C (bubbles) it begins to sinter at 205°C. The dimaleate melts at 188°C to 190°C after sintering from 180°C (recrystallized from methanol). 

Amino acid zwitterions are internal salts and therefore have many of the physical properties associated with salts. They have large dipole moments, are soluble in water but insoluble in hydrocarbons, and are crystalline substances with relatively high melting points. In addition, amino acids are amphiprotic they can react either as acids or as bases, depending on the circumstances. In aqueous acid solution, an amino acid zwitterion is a base that accepts a proton to yield a cation in aqueous base solution, the zwitterion is an add that loses a proton to form an anion. Note that it is the carboxylate, -C02-, that acts as the basic site and accepts a proton in acid solution, and it is the ammonium cation, -NH3+, that acts as the acidic site and donates a proton in base solution. 

Like PEO-LiCl04, a 6 1 crystalline compound is formed but, in this instance, the weakened interactions between polymer chains [18] contributes to the lowest melting point for any PEO-salt crystalline complex. A eutectic with composition 0 Li = 11 1 forms, provided the PEO molecular chain length is beyond the entanglement threshold [31]. For lower molecular weights, the 6 1 compound dose not crystallize in the presence of excess PEO and a crystallinity gap exists over the range 6 l < 0 Li < 12 1 [26]. 

Visual inspechon frequently cannot differenhate between an amorphous or crystalline material, e.g. at Pfizer medicinal chemists were required to submit only crystalline and not amorphous compounds to an automated thermodynamic solubility assay. In prachce half the white powders that they produced for the assay and that they thought were crystalline were actually amorphous. Prior to 2000 the vast majority of these medicinal chemistry labs had no melting point equipment and it was only in 2000 that the pharmaceuhcal sciences department started a workshop to teach medicinal chemists the importance of solid state properhes, how to crystallize compounds and the importance of salt forms. 

Primary aromatic amides are crystalline solids with definite melting points. Upon boiling with 10-20 per cent, sodium or potassium hydroxide solution, they are hydrolysed with the evolution of ammonia (vapour turns red litmus paper blue and mercurous nitrate paper black) and the formation of the alkali metal salt of the acid ... 

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