HF-melamine

A solution of HF/melamine (86 14 w/w) was prepared by gradually dissolving solid melamine (2.1 g. 16.7 mmol) in anhyd HF (12.9 mL, 0.65 mol) in a 100-mL polyethylene reaction vessel with stirring at 0 C. Cyclohexenc (0.5 mL, 5 mmol) dissolved in pentane (3 mL) or CC14 was then added diopwise to the stirred solution. The mixture was further stirred at 0 C for 10 min. The organic layer was then separated (free from HF) and distilled to isolate fluorocyclohexane yield 98-100% bp 100 C. 

Acyl chlorides (or anhydrides) react in 70% hydrogen fluoride/pyridine to give acyl fluorides in high yields31 (for HF/melamine, see ref 248). 

A solution of 86% HF/melamine (15mL) was placed in a 100-mL polyethylene reaction vessel under stirring. Cyclohexene (0.41 g, 5 mmol) in THF (3 mL) was then added dropwise to the solution. The mixture was stirred at 0 C for 1 h. The reaction was then quenched with ice water. The mixture was neutralized with NaHCOj. The yellow milky precipitate formed was separated by filtration this was assigned as the melamine 6 HF complex. The filtrate was extracted with EtjO. The EtjO layer was washed with aq brine, and finally dried (anhyd MgSO ) removal of the solvent gave the product yield 0.50 g (98%) 99.9% isomeric purity. 

Table 4. Hydrofluorination of Cydohexene with HF/Pyridine or HF/Melamine in Various Solvents at 0 C ...

The general concept is that sulfur is introduced into the organic substrate as a direct synthetic precursor of fluorine. Tlte sulfur compound is then treated with a thiophilic, soft electrophilic oxidant, for example electrophilic halogenation agents (NBS, NIS, DBH, Br2, SO2CI2 [148], Fj [149], IF5 [150], BrFj [151], 4-MePhIF2 [152], or nitrosyl cations (NO BF., ) [146] in the presence of a fluoride source (50% or 70% HF-pyridine [143], HF-melamine [144], NEt3 3HF) [147]. 

Hydrolysis of polyamide-based formulations with 6 N HC1 followed by TLC allows differentiation between a-aminocaproic acid (ACA) and hexamethylenedi-amine (HMD) (hydrolysis products of PA6 and PA6.6, respectively), even at low levels. The monomer composition (PA6/PA6.6 ratio) can be derived after chromatographic determination of the adipic acid (AA) content. Extraction of the hydrolysate with ether and derivatisa-tion allow the quantitative determination of fatty acids (from lubricants) by means of GC (Figure 3.27). Further HC1/HF treatment of the hydrolysis residue, which is composed of mineral fillers, CB and nonhydrolysable polymers (e.g. impact modifiers) permits determination of total IM and CB contents CB is measured quantitatively by means of TGA [157]. Acid hydrolysis of flame retarded polyamides allows to determine the adipic acid content (indicative of PA6.6) by means of HPLC, HCN content (indicative of melamine cyanurate) and fatty acid (indicative of a stearate) by means of GC [640]. Determination of ethylene oxide-based antistatic agents... 

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