Monofluorides

Both the binary and complex fluorides of aluminum have played a significant role in the aluminum industry. Aluminum trifluoride [7784-18-17, A1F., and its trihydrate [15098-87-0] 3 3H2O, have thus far remained to be the only binary fluorides of industrial interest. The nonahydrate [15098-89-2] 3 9H2O, and the monohydrate [12252-28-7, 15621 -55-3], AIF 20, are of only academic curiosity. The monofluoride [13595-82-9], AIF, and the difluoride [13569-23-8], AIF2, have been observed as transient species at high temperatures. 

Significant vapor pressure of aluminum monofluoride [13595-82-9], AIF, has been observed when aluminum trifluoride [7784-18-1] is heated in the presence of reducing agents such as aluminum or magnesium metal, or is in contact with the cathode in the electrolysis of fused salt mixtures. AIF disproportionates into AIF. and aluminum at lower temperatures. The heat of formation at 25°C is —264 kJ/mol(—63.1 kcal/mol) and the free energy of formation is —290 kJ/mol(—69.3 kcal/mol) (1). Aluminum difluoride [13569-23-8] h.3.s been detected in the high temperature equihbrium between aluminum and its fluorides (2). 

Bromine Monofluoride. Bromine monofluoride is red to red-brown (4) and is unstable, disproportionating rapidly into bromine and higher fluorides. Therefore, the measurement of its physical properties is difficult and the values reported in Table 1 are only approximate. The uv-absorption spectmm is available (25). 

Chlorine Monofluoride. Chlorine monofluoride is a colorless gas that condenses to a Hquid with a slight yeUow cast and free2es to a white soHd. The infrared spectmm of gaseous chlorine monofluoride and the Raman spectmm of the Hquid have been studied (36). The uv-absorption spectmm (37) and vapor pressure data are also available (11). 

An equiHbrium exists between chlorine trifluoride, chlorine monofluoride, and fluorine gas (38). The equiHbrium constant may be expressed as... 

Chlorine Trifluoride. Chlorine trifluoride is produced commercially by the continuous gas-phase reaction of fluorine and chlorine ia a nickel reactor at ca 290°C. The ratio of fluorine to chlorine is maintained slightly in excess of 3 1 to promote conversion of the chlorine monofluoride to chlorine trifluoride. Sufficient time ia the reactor must be provided to maintain high conversions to chlorine trifluoride. Temperature control is also critical because the equiHbrium shift of chlorine trifluoride to chlorine monofluoride and fluorine is significant at elevated temperatures. 

Ha.logen Fluorides. These include compounds such as IF, IF, GIF, etc, of which only a few, GIF, GIF, BrP, and IF, are used to some extent. They act both as halogen exchange agents and, in the case of the monofluorides, as addition agents to unsaturated bonds (17). 

Fig. 1. Stmcture of poly(carbon monofluoride). , carbon o, fluorine. The interstitial space is 0.66 nm.

Bromine monofluoride [13863-59-7], BrF, can be prepared by the direct reaction of Br2 and F2, but because it readily disproportionates it has never been prepared in pure form (57). However, BrF can be prepared in situ by the reaction of Br2 with AgF in benzene (58) or by the reaction of A/-bromoacetamide and HF in ether (59). BrF adds to simple alkenes at room temperature to give products of trans-addition. Bromine trifluoride [7787-71-5], BrF, can be formed from gaseous fluorine and Hquid bromine (60). Bromine pentafluoride [7789-30-2], BrF, is formed from the reaction of BrF vapor with gaseous fluorine at 200°C (60). The tri- and pentafluorides are commercially available. As strong fluorinating agents they are useful in... 

Graphite fluoride continues to be of interest as a high temperature lubricant (6). Careful temperature control at 627 3° C results in the synthesis of poly(carbon monofluoride) [25136-85-0] (6). The compound remains stable in air to ca 600°C and is a superior lubricant under extreme conditions of high temperatures, heavy loads, and oxidising conditions (see Lubrication and lubricants). It can be used as an anode for high energy batteries (qv). 

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. ... 

Chemical Designations - Synonyms Argentous fluoride Silver monofluoride Chemical Formula AgF. 

When the reaction is carried out in pyridine the mixtures are difficult to separate, but the monofluorides (11) predominate. Joly and Warnant succeeded in preparing the pure 4-monofluoro-A -3-ketones (12) by working in methanol at —20°. The latter are readily isomerized to the A -isoraers (11). 

Hydroxy-4-fluoroestr-4-en-3-one is obtained by rechromatography on Florisil of the combined material of the late eluates from the isolation of the 4,4-difIuoride and the mother liquor from the recrystallization of the latter. Elutions with 1 1 methylene dichloride-ether yield 0.41 g of crude monofluoride mp 143-146°. Recrystallization from hexane-acetone affords 0.29 g of pure monofluoride mp 147-148° [aJo 49° (CHCI3) X 248 m i ( , 15,000). 

The effect of the substituent group can be seen in the reactions of the following senes of halogenated esters Methyl 2,3 dichloro-3-fluoro-2-methylpropionate and chlorine monofluoride first form methyl 2-chloro-3,3-difluoro-2-methylpro-pionate An additional equivalent of chlorine monofluoride produces methyl 2 methyl-2,3,3-trifluoropropionate (equation 14)... 

However, methyl 2,2,3-trichloropropionate and chlorine monofluoride form methyl 2,3 diehloro-2-fluoropropionate An additional equivalent of chlorine monofluoride selectively generates methyl 3-chloro-2,2-difluoropropionate [7i] (equation 15)... 

Chlorine monofluoride can be tamed by reacting it with cyanunc fluoride to form the trimer (CF2NC1)3 The trimer reacts with 1,1-dichloro 2,2,2 tri fluoroethanesulfenyl chloride to form a mixture of 1 chloro-l,2,2,2-tetra-fluoroethanesulfenyl chlonde and perfluoroethanesulfenyl chloride In the same Way, tnfluoroacetyl bromide yields trifluoroacetyl fluonde[14] (equation 16)... 

Chlorine monofluoride m a hydrogen fluoride solution reacts rapidly at low temperature with haloacetate and halopropanoate esters to give 61-80% yields of a a difluoroalkyl ethers [242] (equation 128)... 

Table 1. Primary Monofluorides and a,oi-Difluorides from 2,4,6-Triphenylpyridinium Fluoride and Primary Amines and Diamines [1,2]...

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