Reaction with fluoroformates

At 225—275°C, bromination of the vapor yields bromochloromethanes CCl Br, CCl2Br2, and CClBr. Chloroform reacts with aluminum bromide to form bromoform, CHBr. Chloroform cannot be direcdy fluorinated with elementary flourine fluoroform, CHF, is produced from chloroform by reaction with hydrogen fluoride in the presence of a metallic fluoride catalyst (8). It is also a coproduct of monochlorodifluoromethane from the HF—CHCl reaction over antimony chlorofluoride. Iodine gives a characteristic purple solution in chloroform but does not react even at the boiling point. Iodoform, CHI, may be produced from chloroform by reaction with ethyl iodide in the presence of aluminum chloride however, this is not the route normally used for its preparation. 

The reaction of silyl enol ethers with fluoroformates and fluoroformamides, catalysed by the addition of tetra-n-butylammonium fluoride, produces enol carbonates and carbamates in acceptable yields [60],... 

The iodine atom in the monoiodide may be replaced by other groups and, by reaction with silver salts, for example, As(CF3)2CN (b.p. 89 5°) and As(CFg)2SCN (b.p. 116—118°) are readily prepared. Reaction of the monoiodide with mercury gives the cacodyl As2(CF3)4 (b.p. 106 to 107°), while with mercuric oxide the oxide As2(CF3)40 (b.p. 95—97°) is formed. The chemistry of these substances has not yet been studied in detail, but it is noteworthy that hydrolysis of the perfluorocacodyl gives both fluoroform and fluoride, which parallels the observations made on the diphosphine. 

Fluorodisulfuric acid, salts of, 2 127 Fluoro(fluorosulfuryl) peroxide, 16 138-140 preparation of, 16 138, 139 properties of, 16 139 reactions of, 16 139, 140 Fluoroform, 3 379-380 Fluoroimines, preparation, 33 185 Fluorooximes, reaction with hexafluoroacetone, 30 271... 

Both aromatic and aliphatic fluoroformates 7 can be readily prepared from phenols or alcohols and carbonyl difluoride and treated with sulfur tetrafluoride without isolation. Hydrogen fluoride evolved in the reaction of hydroxy compounds with carbonyl di fluoride serves as a catalyst for the consecutive reaction with sulfur tetrafluoride.15<)-162 This provides a general, convenient, direct synthesis of aryl and alkyl trifluoromethyl ethers 5 from phenols and alcohols. When the intermediate fluoroformate 7 is isolated prior to treatment with sulfur tetrafluoride, at least one mole equivalent of hydrogen fluoride is necessary to promote the fluorination reaction. 159 163 Representative examples of the conversion of hydroxy compounds 6 into trifluoromethyl ethers 5 via intermediate fluoroformates 7 are given (for other examples 7 -> 5, see Houben-Weyl, Vol. E4, pp 628. 629). 

The process and mechanism for nucleophilic transfer from MesSiCFs to electrophilic sites are analogous to the clever use of DMF as a reservoir for trifluoromethide (10.45A), formed by reaction of fluoroform with a base [96], in a process outlined in Figure 10.45 they are also analogous to the use of iodoperfluoroalkanes with tetrakis(dimethylami-no)ethene [99] (Figure 10.46). 

One of the first representative reaction with hard nucieophiies we deveioped was the reaction of 1-chloroai-kyl carbonates with fiuorides anion. This reaction proceeds through A1 attack mechanism, which is in accord to the H5AB theory, thus converting 1-chioroalkyi carbonates to fluoroformates in good yields (Ref. 91). 

Treatment of enolizable aldehydes with fluoroformates and KF in DMSO (55-100°C for 15-24 h) afforded 1-alkenyl carbonates in 72-92 % yield. According to Olofson s studies, the activated fluoride anion acting as a base deproto-nates the aldehyde to yield an enolate which reacts rapidly with the fluoroformate to give the desired vinylic carbonate as shown in scheme 99 (Ref. 131). Excess KF neutralises the HF which is liberated in the reaction as KHF2. 

Scheme 99 Mechanism of the reaction of fluoroformates with aldehydes in presence of KF in DMSO.

Reaction with phenols and alcohols. Carbonyl fluoride reacts with a phenol or alcohol (autoclave, 100-200°) to form the fluoroformate (10). In a second step the fluoroformate on reaction with sulfur tetrafluoride (150-200°) affords the aryl(alkyl) trifluoromethyl ether. ... 

Carbonyl difluoride is a particularly versatile fluorinating agent, and an important material for the synthesis of organofluorine compounds [1079], Its reactions with perfluoroalkenes gives perfluoroacyl fluorides in the presence of a fluoride ion source, and its facile reaction with amines or alcohols results in the formation of carbamoyl fluorides or fluoroformates, respectively. The fluorination of carbonyl compounds, such as aldehydes and ketones, with COF can give gem-difluorides by replacement of the carbonyl oxygen atom with two atoms of fluorine e.g.-. 

Although, supercritical carbon dioxide has the advantage of being nontoxic and abundant, it is practically immiscible with water. Therefore, supercritical fluids used as the reaction medium in enzyme-catalyzed reactions include fluoroform, sulfur hexafluoride, and ethane, while lipases are the enzymes utilized in such reactions. ... 

An alternative means of technical-scale access to fluoroarenes is the fluoroformate method. Starting from the corresponding phenol a fluoroformate is generated by reaction with carbonyl chloride fluoride and subsequently catalytically decarboxy-lated to the aryl fluoride, in the gas phase, by contact with hot platinum [80] (Scheme 2.30). A newer, greener variant of the fluoroformate process has recently been introduced by Rhodia. In this the fluoroformate is formed by the (catalyzed) reaction of the phenol with COj in HF, and the expensive platinum catalyst is replaced by an aluminum-based material. 

FLUOROFORM (75-46-7) Violent reaction with alkaline earth and alkali metals. Reacts violently with aluminum oxide at elevated temperatures, producing hydrogen chloride and phosgene vapors. Incompatible with beryllium, decaborane, diborane, difluoromethylene dihypofluorite, fluorine, lithium, magnesium, potassium, potassium acetylene-1,2-dioxide, potassium acetylene-1,2-dioxide, potassium-sodium alloy, sodium amide, titanium, uranium hydride, zinc. Attacks aluminum, magnesium, zinc, and their alloys. 

The kinetic parameters of the reaction of methoxy with fluoroform [293] were derived from experimental data for the reverse reaction and the calculated equilibrium constant (see Section 13.7). 

Kamat et al. found that the initial transesterification rate with Candida cylin-dracea lipase decreased markedly upon increasing the pressure from 80 to 120 bar [5]. They ran the reaction in fluoroform at 50 °C and calculated the apparent activation volume of the reaction from initial reaction rates at different pressures. The apparent activation volume showed a maximum near the critical point of fluoroform. As the pressure increased from 60 to 180 bar the apparent activation volume approached zero and the reaction rate decreased to one tenth. 

HF reaction with 3-chloro-pentafluoro-l-propene (CF2=CF-CF2C1) at 200°C, catalyzed by activated carbon, yields HFP. l Hexafluoropropylene can be prepared from the catalytic degradation of fluoroform (CHF3) at 800-1000°C in a platinum-lined nickel re-actor.l l Another method is copyrolysis of fluoroform and chlorotrifluoroethylene (CF2=CFCl),f l or chlorodifluoromethane and l-chloro-1,2,2,2-tetrafluoroethane (CHClFCFg), giving good yields of HFP. 

Low-temperature reaction of the model compound 1,1,2,2-tetrafluoroethylbis-(trifluoromethyl)phosphine with one equivalent of bromine and pyrolysis of the product gave a complex mixture containing bromotrifluoromethane, starting material, and other products but after the bromination-pyrolysis sequence had been repeated twice more, the major products were 1-bromo-1,1,2,2-tetrafluoroethane (98%), and bromotrifluoromethane (74%), together with fluoroform (11%) and a similar amount of bromodifluoromethane. 

Depending on the ring substituent, trifluoromethoxyben2enes can be made by the sequential chlorination—fluorination of anisole(s) (351—354). A one-step process with commercial potential is the BF (or SbF2)-cataly2ed reaction of phenol with carbon tetrachloride/hydrogen fluoride (355). Aryl trifluoromethyl ethers, which may not be accessible by the above routes,may be made by fluorination of aryl fluoroformates or aryl chlorothioformates with sulfur tetrafluoride (348) or molybdenum hexafluoride (356). 

Reactions that have led to other deoxyhalogeno sugars do not necessarily lead to deoxyfluoro sugars, as, for example, in the attempted decomposition of fluoroformates, the treatment of diazoketones and of 2-deoxy-2-diazohexonates with hydrogen fluoride, and the reaction of benzoxonium ions with halide ions. The reaction2281229 by which fluoroformates are thermally or catalytically decarbonylated to give alkyl fluorides has been applied to carbohydrates. Both thermal and catalytic treatment of 6-0-(fluoroformyl)-l,2 3,4-di-0-isopropylidene-... 

Goswami and Sarkar3 claimed to have prepared methyl and ethyl fluoroformates by the action of thallium fluoride on the corresponding chloroformates. These fluoroformates were described as powerful lacrimators. We found that no appreciable reaction took place between potassium fluoride and ethyl chloroformate in boiling carbon tetrachloride or nitrobenzene. Ethyl fluoroformate could, however, be readily produced by the action of potassium fluoride on ethyl chloroformate by using the autoclave technique. It was found not to have the lacrimatory properties claimed for it, and was non-toxic in comparison with M.F.A. This non-toxicity was to be expected, as the fluoroformate contains the COF and not the CH2F- group. 

Many solvent properties are related to density and vary with pressure in a SCF. These include the dielectric constant (er), the Hildebrand parameter (S) and n [5], The amount a parameter varies with pressure is different for each substance. So, for example, for scC02, which is very nonpolar, there is very little variation in the dielectric constant with pressure. However, the dielectric constants of both water and fluoroform vary considerably with pressure (Figure 6.3). This variation leads to the concept of tunable solvent parameters. If a property shows a strong pressure dependence, then it is possible to tune the parameter to that required for a particular process simply by altering the pressure [6], This may be useful in selectively extracting natural products or even in varying the chemical potential of reactants and catalysts in a reaction to alter the rate or product distributions of the reaction. 

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