Reactions fluorine

Simple Fluorination Reactions. Some examples (62) of O2F2 acting mainly as a fluotinating agent are... 

The fluorination reaction is best described as a radical-chain process involving fluorine atoms (19) and hydrogen abstraction as the initiation step. If the molecule contains unsaturation, addition of fluorine also takes place (17). Gomplete fluorination of complex molecules can be conducted using this method (see Fluorine compounds, organic-direct fluorination). 

This reaction has often reached explosive proportions in the laboratory. Several methods were devised for controlling it between 1940 and 1965. For fluorination of hydrocarbons of low (1—6 carbon atoms) molecular weight at room temperature or below by these methods, yields as high as 80% of perfluorinated products were reported together with partially fluorinated species (9—11). However, fluorination reactions in that eta involving elemental fluorine with complex hydrocarbons at elevated temperatures led to appreciable cleavage of the carbon—carbon bonds and the yields invariably were only a few percent. 

Thus, for a successful fluorination process involving elemental fluorine, the number of coUisions must be drasticaUy reduced in the initial stages the rate of fluorination must be slow enough to aUow relaxation processes to occur and a heat sink must be provided to remove the reaction heat. Most direct fluorination reactions with organic compounds are performed at or near room temperature unless reaction rates are so fast that excessive fragmentation, charring, or decomposition occurs and a much lower temperature is desirable. 

The reaction with fluorine occurs spontaneously and explosively, even in the dark at low temperatures. This hydrogen—fluorine reaction is of interest in rocket propellant systems (99—102) (see Explosives and propellants, propellants). The reactions with chlorine and bromine are radical-chain reactions initiated by heat or radiation (103—105). The hydrogen-iodine reaction can be carried out thermally or catalyticaHy (106). 

The recent discovery of a convenient synthesis of sulfur tetrafluoride from sulfur dichloride and sodium fluoride in acetonitrile invited the application of this reagent in fluorination reactions. Hasek, Smith and Engelhardt showed that carboxylic acids and their derivatives can be converted into trifluoromethyl derivatives and that aldehydes and ketones are converted into 5 em-difluoro compounds. They also observed that the reaction was acid... 

Mixtures of anhydrous hydrogen fluoride and tetrahydrofuran are successfully used as fluorinating agents to convert 1,1,2-trifluoro-l-allcen-3-ols, easily prepared from bromotrifluoroethene via lithiation followed by the reaction with aldehydes or ketones, to 1,1,1,2-tetrafluoro-2-alkenes The yields are optimal with a 5 1 ratio of hydrogen fluoride to tetrahydrofuran The fluorination reaction involves a fluonde lon-induced rearrangement (Sf,j2 mechanism) of allylic alcohols [65] (equation 40)... 

A variety of media have been used for the Wallach fluorination reaction anhydrous hydrogen fluoride alone or with cosolvents such as methylene chloride, benzene, or tetrahydrofuran and hydrogen fluoride-pyridine alone or with co solvents such as benzene, glyme, or acetic acid [42,43, 46 50] Solutions of cesium fluoride, tetraethylammonium fluoride, or tetrabutylammonium fluoride in strong acids such as methanesulfonic acid or trifiuoroacetic acid with numerous cosolvents have also been studied [48, 49]... 

Diazoketones that are readily prepared from acyl chlorides and diazomethane [92] also undergo a variety of fluorination reactions... 

The fluorination reactions considered so far can be categorized as metathesis, oxidation or substitution, Occasionally reductive fluorination is the preferred route to a lower fluoride. Examples are ... 

F3CIO tends to react slowly at room temperature but rapidly on heating or under ultraviolet irradiation. Typical of its fluorinating reactions are ... 

In recent years, fluorine bomb calorimetry has been used effectively. A number of substances that will not burn in oxygen will burn in fluorine gas. The heat resulting from this fluorine reaction can be used to calculate AfH°m. For example, Murray and 0 Hare have reacted GeS2 with fluorine and measured ArH°. The reaction is... 

The first successful, fluorine reaction observed with organome-tallics was the conversion of dimethylmercury into bis(trifluoro-methyDmercury (25). 

The fluorination of CF3CH2CI into CF3CH2F over chromium oxides is accompanied by a dehydrofluorination reaction (formation mainly of CF2=CHC1). This dehydrofluorination is responsible for the deactivation of the catalyst. A study of the dehydrofluorination reaction of CF3CH2CI proves that the reaction is favoured when the degree of fluorination of chromium oxide increases. Consequently it would be favoured on strong acid sites. Adding nickel to chromium oxide decreases the formation of alkenes and increases the selectivity for fluorination while the total activity decreases. Two kinds of active sites would be present at the catalyst surface. The one would be active for both the reactions of dehydrofluorination and of fluorination, the other only for the fluorination reaction. 

The aim of our work is to study, under adequate operating conditions, the dehydrofluorination reaction of CF3CH2CI so as to determine the nature of the sites involved in the 6uorination and the dehydrofluorination of CF3CH2CI. Thus a selective poisoning of dehydrofluorination sites would allow to increase the selectivity for the fluorination reactions. 

Consequently the catalytic activity for the CF3CH2CI fluorination reaction was measured in the presence of an excess of HF in a fixed bed dynamic reactor (fig. 2). 

The catalyst deactivation was then low, CF3CH2F being preponderantly formed. CF2=CHC1 is the only alkene formed.In those conditions the formation of this alkene is at the equilibrium state. The catalytic activity for the fluorination reaction was calculated after a 2 hour reaction. 

However the dehydrofluorination reaction compared to the fluorination reaction is favoured. The ratio between the catalytic activity for the fluorination reaction and the... 

The presence of nickel did not affect the specific surface, nevertheless the activity for the fluorination reaction decreased particularly for the catalyst with 10 % nickel. 

Moreover a significant decrease in the formation of alkenes could be observed for the Ni-Cr catalysts. Consequently the presence of nickel dis voured the dehydrofluorination reaction while increasing the selectivity for the fluorination reaction. 

Thus when the degree of fluorination increased, the selectivity for the fluorination reaction decreased. The dehydrofluorination reaction required the rupture of the C-F bond of the CF3CH2CI molecule while the fluorination reaction involved the rupture of the C-Cl bond. The C-F bond being harder to split than the C-Cl bond [11], the dehydrofluorination reaction require stronger adsorption sites than the fluorination reaction. 

The nickel addition in chromium oxide decreased the formation of alkenes which was smaller than the one observed in the presence of just chromium oxide. It is to be remarked that the decrease of alkene formation was independent of the quantity of nickel in the catalyst. However, the catalytic activity for the fluorination reaction decreased when the nickel content increased. Thus the addition of nickel in small quantities allowed to increase the selectivity for the fluorination reaction. We could suggest that nickel substitute... 

Thus, it would be possible to increase the selectivity for the fluorination reaction, nethertheless, this would induce a decrease of the catalytic activity. 

The micro reactor was specially made for fluorination reactions. Before carrying out the fluorination reactions, passivity of the micro reactor has to be ensured by exposure of the micro channel to increasing concentrations of fluorine in nitrogen [16]. 

More complicated are fluorination reactions of phosphorus pentoxide with NH F 34) and NaHp2 (55) yet they are suited for the preparation of fluorophosphates on large scale ... 

Methyl 2-bromo-5,5-(ethylenedioxy)[2.2.1]bicycloheptane-7-carboxylate Wang, C.-L. J. et al., J. Chem. Soc., Chem. Comm., 1976, 468 In an attempt to improve isomer distribution from the fluorination reaction, one run was cooled to below —40°C, but on quenching with water, a violent explosion occurred. 

Though a powerful oxidant, the difluoride is not explosively unstable. Safe procedures for the use of xenon difluoride in fluorination reactions are detailed. Residual traces of the fluoride are rapidly destroyed by dichloromethane at ambient temperatures. 

Fluorosulfonic acid can be used in fluorination reactions, and it functions as a catalyst in reactions such as alkylation and polymerization. One of the most important uses of FS03H and C1S03H is as sulfonating agents to introduce the -S03H group into various organic materials. 

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