Fluorides ammonium

In 1973 the Semiconductor Equipment and Materials Institute (SEMI) held its first standards meeting. SEMI standards are voluntary consensus specifications developed by the producers, users, and general interest groups in the semiconductor (qv) industry. Examples of electronic chemicals are glacial acetic acid [64-19-7] acetone [67-64-17, ammonium fluoride [12125-01 -8] and ammonium hydroxide [1336-21 -6] (see Ammonium compounds), dichloromethane [75-09-2] (see Cm.OROCARBONSANDcm.OROHYDROCARBONs), hydrofluoric acid [7664-39-3] (see Eluorine compounds, inorganic), 30% hydrogen peroxide (qv) [7722-84-1] methanol (qv) [67-56-1] nitric acid (qv) [7697-37-2] 2-propanoI [67-63-0] (see Propyl alcohols), sulfuric acid [7664-93-9] tetrachloroethane [127-18-4] toluene (qv) [108-88-3] and xylenes (qv) (see also Electronic materials). 

In addition, there are other methods of manufacture of cryoHte from low fluorine value sources, eg, the effluent gases from phosphate plants or from low grade fluorspar. In the former case, making use of the fluorosiHcic acid, the siHca is separated by precipitation with ammonia, and the ammonium fluoride solution is added to a solution of sodium sulfate and aluminum sulfate at 60—90°C to precipitate cryoHte (26,27) ... 

Two well-known salts of ammonia (qv) are the normal ammonium fluoride [12125-01 -8] NH F, and ammonium bifluoride [1341 -49-7] NH4HF2 the latter is sometimes named ammonium acid, or hydrogen difluoride. Much of the commercial interest in the ammonium fluorides stems from their chemical reactivity as less ha2ardous substitutes for hydrofluoric acid. 

Ammonium fluoride is a white, deflquescent, crystalline salt. It tends to lose ammonia gas to revert to the more stable ammonium bifluoride. Its solubiUty in water is 45.3 g/100 g of H2O at 25°C and its heat of formation is —466.9 kJ/mol ( — 116 kcal/mol). Ammonium fluoride is available principally as a laboratory reagent. If it is needed in large quantities, one mole of aqueous ammonia can be mixed with one mole of the more readily available ammonium bifluoride (1). 

Manufacture. Anhydrous ammonium bifluoride containing 0.1% H2O and 93% NH4HF2 can be made by dehydrating ammonium fluoride solutions and by thermally decomposing the dry crystals (7). Commercial ammonium bifluoride, which usually contains 1% NH F, is made by gas-phase reaction of one mole of anhydrous ammonia and two moles of anhydrous hydrogen fluoride (8) the melt that forms is flaked on a cooled dmm. The cost of the material in 1992 was 1.48/kg. 

Ammonium fluorides react with many metal oxides or carbonates at elevated temperatures to form double fluorides eg,... 

PbF2 is readily prepared by the action of hydrogen fluoride on lead hydroxide, lead carbonate, or a-lead oxide. It can also be obtained by precipitation from lead nitrate or lead acetate solutions using potassium fluoride, ammonium fluoride, or ammonium bifluoride. 

Manufacture and Economics. Nitrogen tritiuoride can be formed from a wide variety of chemical reactions. Only two processes have been technically and economically feasible for large-scale production the electrolysis of molten ammonium acid fluoride and the direct fluorination of the ammonia in the presence of molten ammonium fluoride. In the electrolytic process, NF is produced at the anode and H2 is produced at the cathode. In a divided cell of 4 kA having nickel anodes, extensive dilution of the gas streams with N2 was used to prevent explosive reactions between NF and H2 (17). 

Phosphoms oxyfluoride is a colorless gas which is susceptible to hydrolysis. It can be formed by the reaction of PF with water, and it can undergo further hydrolysis to form a mixture of fluorophosphoric acids. It reacts with HF to form PF. It can be prepared by fluorination of phosphoms oxytrichloride using HF, AsF, or SbF. It can also be prepared by the reaction of calcium phosphate and ammonium fluoride (40), by the oxidization of PF with NO2CI (41) and NOCl (42) in the presence of ozone (43) by the thermal decomposition of strontium fluorophosphate hydrate (44) by thermal decomposition of CaPO F 2H20 (45) and reaction of SiF and P2O5 (46). 

Difluorophosphates. Difluorophosphates have limited appHcations largely because of hydrolytic instabiHty of the P03F 2 ion. The ammonium salt can be prepared from ammonium fluoride and phosphoric anhydride. 

Ammonium fluorosulfate is produced from ammonium fluoride by reaction with sulfur trioxide, oleum, or potassium pyrosulfate, 1 2820 (48). Solutions of ammonium fluorosulfate show Htfle evidence of hydrolysis and the salt may be recrystallized from hot water. Ammonium fluorosulfate absorbs anhydrous ammonia to form a series of Hquid amines that contain 2.5—6 moles of ammonia per mole of salt (77). 

Fluoroaromatics are produced on an industrial scale by diazotization of substituted anilines with sodium nitrite or other nitrosating agents in anhydrous hydrogen fluoride, followed by in situ decomposition (fluorodediazoniation) of the aryldiazonium fluoride (21). The decomposition temperature depends on the stabiHty of the diazonium fluoride (22,23). A significant development was the addition of pyridine (24), tertiary amines (25), and ammonium fluoride (or bifluoride) (26,27) to permit higher decomposition temperatures (>50° C) under atmospheric pressure with minimum hydrogen fluoride loss. 

Bromo or chloro-2,6-difluoropyridines can be prepared in 50% yield by diasotization of the corresponding 3-halo-2,6-diarninopyridine in ammonium fluoride—hydrogen fluoride solvent (371). 5-Chloro-2,3-difluoropyridine [89402-43-7], a precursor to the herbicide pyroxofop [105512-06-9], was synthesized by a multistep sequence based on aHyl chlorodifluoroacetate [118337-48-7], C1CF2C02-CH2CH=CH2 (415). 

Ammonium fluorohafnate [1692 -24-9], (NH4)2HfFg, or potassium fluorohafnate [16871 -86-6], K HfF, can be prepared by crystallisation from an aqueous hydrofluoric acid solution by addition of ammonium fluoride or potassium fluoride, respectively. 

Diphenylamine can also be produced by passing the vapors of aniline over a catalyst such as alumina, or alumina impregnated with ammonium fluoride (17). The reaction is carried out at 480°C and about 700 kPa (7 atm). Conversion per pass, expressed as parts diphenylamine per 100 parts of reactor effluent, is low (18—22%), and the unconverted aniline must be recycled. Other catalysts disclosed for the vapor-phase process are alumina modified with boron trifluoride (18), and alumina activated with boric acid or boric anhydride (19). 

The vapor-phase conversion of aniline to DPA over a soHd catalyst has been extensively studied (18,22). In general, the catalyst used is pure aluminum oxide or titanium oxide, prepared under special conditions (18). Promoters, such as copper chromite, nickel chloride, phosphoric acid, and ammonium fluoride, have also been recommended. Reaction temperatures are usually from 400 to 500°C. Coke formed on the catalyst is removed occasionally by burning. In this way, conversions of about 35% and yields of 95% have been reported. Carba2ole is frequently a by-product. 

Precipitated siUcas having properties matching those from the conventional sodium siUcate route are said to be possible (79). The hydrofluosiUcic acid that is generated can be recycled ia the system, or can be used to manufacture sodium siUcofluoride or ammonium fluoride. 

The impure product is dissolved in methanol. Subsequent reaction with ammonium fluoride forms ammonium hexafluorotitanate. This soHd, obtained in high purity, reacts with water vapor in a stream of air at 250°C to give anatase. 

Chemical Designatioiis - Synonyms Acid Ammonium Fluoride, Ammonium Acid Fluoride, Ammonium Hydrogen Fluoride Chemical Formula NH NF. ... 

Chemical Designations - Synonyms Neutral Ammonium Fluoride Chemical Formula NH F. Observable Characteristics - Physical State (as normally shipped) Solid Color White Odor None. Physical and Chemical Properties - Physical State at 15 X and I atm. Solid Molecular Weight 37.04 Boiling Point at I atm. Not pertinent (decomposes) Freezing Point Not pertinent Critical Temperature Not pertinent Critical Pressure Not pertinent ecific Gravity 1.32 at 25°C (solid) Vapor (Gas) Density Not pertinent Ratio of Specific Heats of Vapor (Gas) Not pertinent Latent Heat of Vaporization Not pertinent Heat cf Combustion Not pertinent Heat of Decomposition Not pertinent. 

AMMO 2.5 EC , cypermetlu-in, 13 Ammonia, 13 Ammonium acetate, 13 Ammonium arsenate, 13 Ammonium benzoate, 13 Ammonium bicarbonate, 13 Ammonium bifluoride, 14 Ammonium bisulfite, 14 Ammonium carbamate, 14 Ammonium carbonate, 14 Ammonium chloride, 14 Ammonium chlorplatmate, 14 Ammonium clu omate, 14 Ammonium citrate, 14 Ammonium diclu omate, 14 Ammonium fluoride, 14 Ammonium fomiate, 15 Ammonium hexafluorosilicate, 15 Ammonium hydroxide, 15 Ammonium metavanadate, 15 Ammonium molybdate, 15 Ammonium nitrate, 15 Ammonium oxalate, 15 Ammonium perfluorooctanoate, 15 Ammonium persulfate, 15 Ammonium phosphate, 15 Ammonium picrate, 16 Ammonium salicylate, 16... 

Chemistry of Organic Fluorine Compounds II Table 2. Ammonium Fluorides... 

Chloromethoxy-1,2,2 2-tetrafluoroethane is converted by triethylammonium fluoride or piperidine hydrogen fluoride to fluoromethoxy 1 2,2,2-tetra-fluoroethane in greater than 60% yield Piperidine hydrogen fluoride or butyl-ammonium fluoride can convert methoxy-l-chloro-2,2,2-trifluoroethane to methoxy-1,2,2,2-tetrafluoroethane in 80% yield [79]... 

Epoxides are regio- and stereoselectively transformed into fluorohydrins by silicon tetrafluoride m the presence of a Lewis base, such as diisopropyleth-ylamme and, m certain instances, water or tetrabutylammonium fluoride The reactions proceed under very mild conditions (0 to 20 C in 1,2-diohloroethane or diethyl ether) and are highly chemoselective alkenes, ethers, long-chain internal oxiranes, and carbon-silicon bonds remain intact The stereochemical outcome of the epoxide ring opening with silicon tetrafluoride depends on an additive used, without addition of water or a quaternary ammonium fluoride, as fluorohydrins are formed, whereas m the presence of these additives, only anti opening leading to trans isomers is observed [17, 18] (Table 2)... 

Benzyl and alkyl tnalkylsilyl ethers undergo clean fluonnation to give good yields of benzyl and alkyl fluorides, respectively, when reacted with a combination of d quaternary ammonium fluoride and methanesulfonyl orp- toluenesulfonyl fluoride. The reactions are applicable strictly to a primary carbon-oxygen bond, secondary and tertiary alkyl silyl ethers remain intact or, under forcing conditions, aie dehydrated to olefins [29] (equation 22)... 

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