Fluorides alkyl

Primary, secondary, and tertiary alcohols can be converted directly to fluorides, usually in high yield, by treatment with a mixture of perfluoro-1-butanesulfonyl fluoride (PBSF), triethylamine tris(hydrogen fluoride), and triethylamine (Eq. 6.56) [87]. This combination of reagents tolerates other functionality and the base present neutralizes HE as it forms. 

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Alkyl fluorides may be prepared in moderate yield by interaction of an alkyl bromide with anhydrous potassium fluoride in the presence of dry ethylene glycol as a solvent for the inorganic fluoride, for example ... 

CAUTION Alkyl fluorides are said to he highly toxic. Great care should be taken not to inhale the vapours. 

Chapter III. 1 Heptene (111,10) alkyl iodides (KI H3PO4 method) (111,38) alkyl fluorides (KF-ethylene glycol method) (111,41) keten (nichrome wire method) (111,90) ion exchange resin catalyst method for esters (111,102) acetamide (urea method) (111,107) ethyl a bromopropionate (111,126) acetoacetatic ester condensation using sodium triphenylmethide (111,151). 

Concerning my research during my Dow years, as I discuss iu Chapter 4, my search for cationic carbon intermediates started back in Hungary, while 1 was studying Friedel-Crafts-type reactions with acyl and subsequently alkyl fluorides catalyzed by boron trifluoride. In the course of these studies I observed (and, in some cases, isolated) intermediate complexes of either donor-acceptor or ionic nature. 

Density Alkyl fluorides and chlorides are less dense and alkyl bromides and iodides more dense than water... 

The order of reactivity of the hydrogen halides parallels their acidity HI > HBr > HCl >> HF Hydrogen iodide is used infrequently however and the reaction of alco hols with hydrogen fluoride is not a useful method for the preparation of alkyl fluorides Among the various classes of alcohols tertiary alcohols are observed to be the most reactive and primary alcohols the least reactive... 

Because the carbon-halogen bond breaks m the slow step the rate of the reaction depends on the leaving group Alkyl iodides have the weakest carbon-halogen bond and are the most reactive alkyl fluorides have the strongest carbon-halogen bond and are the least reactive... 

Among alkyl halides alkyl iodides undergo nucleophilic substitution at the fastest rate alkyl fluorides the slowest... 

The order of alkyl halide reactivity in nucleophilic substitutions is the same as their order m eliminations Iodine has the weakest bond to carbon and iodide is the best leaving group Alkyl iodides are several times more reactive than alkyl bromides and from 50 to 100 times more reactive than alkyl chlorides Fluorine has the strongest bond to car bon and fluonde is the poorest leaving group Alkyl fluorides are rarely used as sub states m nucleophilic substitution because they are several thousand times less reactive than alkyl chlorides... 

We saw m Section 8 2 that the rate of nucleophilic substitution depends strongly on the leaving group—alkyl iodides are the most reactive alkyl fluorides the least In the next section we 11 see that the structure of the alkyl group can have an even greater effect... 

In media such as water and alcohols fluoride ion is strongly solvated by hydro gen bonding and is neither very basic nor very nucleophilic On the other hand the poorly solvated or naked fluoride 10ns that are present when potassium fluoride dis solves m benzene m the presence of a crown ether are better able to express their anionic reactivity Thus alkyl halides react with potassium fluoride m benzene containing 18 crown 6 thereby providing a method for the preparation of otherwise difficultly acces sible alkyl fluorides... 

In contrast to nucleophilic substitution m alkyl halides where alkyl fluorides are exceedingly unreactive aryl fluorides undergo nucleophilic substitution readily when the ring bears an o or a p nitro group... 

With alcohols, mixtures of alkyl fluorides and alkyl ethers are obtained (100). Alcohols beating electron-withdrawiag groups can be converted to the corresponding fluorides ia high yield (101). Sulfur tetrafluoride replaces the carboayl oxygea with fluorine (100,102). 

Alkyl fluorides have been prepared by reaction between elementary fluorine and the paraffins, by the addition of hydrogen fluoride to olefins, by the reaction of alkyl halides with mercurous fluoride, with mercuric fluoride, with silver fluoride, or with potassium fluoride under pressure. The procedure used is based on that of Hoffmann involving interaction at atmospheric pressure of anhydrous potassium fluoride with an alkyl halide in the presence of ethylene glycol as a solvent for the inorganic fluoride a small amount of olefin accompanies the alkyl fluoride produced and is readily removed by treatment with bromine-potassium bromide solution. Methods for the preparation of alkyl monofluorides have been reviewed. ... 

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)... 

Alkyl Fluoride Alkene Ether Phos- phonaie... 

Lower aliphatic primary alcohols including octanol, halogeno alcohols, and benzylic alcohols yield only alkyl fluorides [81, 82 The reaction of higher primary alcohols gives a mixture of fluorides and alkyl 2,3,3,3-tetrafluoropropionates [S3] and 2-nitro alcohols, alcohols branched at C-2 [82, 84 and unsaturated alcohols [55] give 2,3,3,3-tetrafluoropropionates exclusively... 

Simple alkyl fluorides can be converted to alkyl iodides with iodotrimethyl-silane [7/]. 

Alkyl fluorides are more reactive than other alkyl halides under Friedel-Crafts conditions, whereas trifluoromethyl groups are less reactive than other trihalomethyl groups Thus, a bromoindane is prepared from 1-bromo-l-fluoro-2,2,3,3-tetramethylcyclopropane and benzene [5] (equation 8) whereas 3-tnfluo romethylphenyldiphenylchloromethane is obtained from 3-trifluoromethyl-benzotrichloride and benzene [9] (equation 9)... 

The reactions of some fluorinated ethers may result in the elimination of alkyl fluorides In the case of 2-methoxyperfluoro-2-butene, treatment with antimony pentafluoride gives perfluoro-3-buten-2-one and methylfluoride [107] By reacting 2-chloro-l,l,2-trifluorodiethyl ether with boron trifluoride etherate or with aluminum chloride, chlorofluoroacetyl fluoride can be obtained with the elimination of ethyl fluonde [108] (equations 76 and 77)... 

Alkyl fluoride (slowest rate of elimination strongest carbon-halogen bond)... 

Cyclohexyl bromide, for exfflnple, is converted to cyclohexene by sodium ethoxide in ethanol over 60 times faster than cyclohexyl chloride. Iodide is the best leaving group in a dehydrohalogenation reaction, fluoride the poorest. Fluoride is such a poor leaving group that alkyl fluorides are rarely used as starting materials in the preparation of alkenes. 

Alkyl fluorides can be prepared by the Finkelstein reaction. The fluoride anion is a bad leaving group the reverse reaction thus does not take place easily, and the equilibrium lies far to the right. As reagents potassium fluoride, silver fluoride or gaseous hydrogen fluoride may be used. 

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