I
Fluoro Alcohols Building Blocks f o r .
b b
I
..
Chemically stable surface active agents High temperature lubricants
T E L O M E R I Z A T I O N of tetrafluoroethylene in methanol in the presence of a free radical initiator produces a series of highly fluorinated alcohols of the general formula: H ( C F Z C F ~ ) . C H ~ O H . This technique offers a convenient source of highly fluorinated compounds containing a useful functional group. The tetrafluoroethylene-methanol telomer alcohols have a linear perfluoroalkyl chain containing a n even number of -CF2groups and having a hydrogen atom a t one end and a hydroxymethyl group at the other. No branching of the fluoroalkyl chain has been observed. Where radical, R., is formed from an initiator such as di-tert-butyl peroxide, the postulated over-all series of reactions to form these alcohols is:
+ R . RH + .CHzOH + CFz=CFt CFzCFzCHzOH .CFzCF?CHtOH + ( n - l)CFt=CF2 + ,(CFzCFz),CHzOH .(CF2CFz),CHzOH + CHaOH CHaOH
.CH*OH
+
-+ '
.-*
H(CFzCFz),CHzOH
+ +CHzOH
The reaction is governed by the general principles of chain transfer. Short chain alcohols are favored by a large excess of methanol and a relatively high initiator concentration. T h e reaction can be carried out conveniently to produce high yields of the lower alcohols, n = 1 to 6, by using an excess of methanol and a peroxide initiator at a temperature where its half life is 1 to 4 hours. Temperatures from 80' to 200' C. and tetrafluoroethylene pressures from 15 to 3000 pounds have been used. The reaction temperature, pressure, and initiator concentration are determined by the necessary safety precautions. Hazards of handling tetrafluoroethylene at high temperatures and pressures have been described (7). The reaction to produce fluoro alcohols is rapid and highly exothermic, and the heat evolved is usually dissipated by using excess methanol and a soluble initiator. For maximum safety, a n electrically heated, high pressure stainless steel autoclave equipped with an efficient stirrer, an internal cooling coil, and a rupture disk is used. The autoclave is located in a barricaded area and has remote controls. Oxygen is carefully excluded during the compression of
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DONALD R. BAER Jackson Laboratory, Organic Chemicals Department
E. 1. du Pont de Nemours and Co., Wilmington, Del.
Dielectric fluids Chemically inert finishes and elastomeric coatings
tetrafluoroethylene and sufficient methanol is maintained in the autoclave to keep the reaction mass fluid. Di-tertbutyl peroxide is used as the initiator in concentrations of 1% or less. Higher concentrations, though favoring shorter product chain lengths, lead to control difficulties during efficient operation.
Properties of TetrafluoroethyleneMethanol Telomer Alcohols Melting points of the solid alcohols increase i n a regular fashion but the liquid alcohols show an anomalous behavior
- 15 ... - 14
Separation and Properties T h e C3 through c13 alcohols (n = 1 to 6) are separated from the mixture of telomerization products by fractional distillation. C15 to C1, (n = 7, 8) alcohols are isolated from the high boiling residue by extraction and crystallization. The alcohols are identified by elementary analysis, infrared and nuclear magnetic resonance spectra, preparing derivatives, and oxidation to acids (70). The lower members (n = 1 to 3) are colorless liquids with low melting points, whereas the higher homologs are white crystalline solids. The C3 alcohol crystallizes readily a t -15' C.; C6 alcohol does not crystallize on standing a t -65' C., and CT alcohol melts at - 14' C. The fluoro alcohols are soluble in polar solvents such as methanol, acetic acid, and ether; less soluble in nonpolar solvents such as benzene, toluene, chloroform, and carbon tetrachloride, C Salcohol (n = 1) is miscible with water.
Chemical Properties The aH,aH,wH-perfluoro alcohols undergo a number of reactions characteristic of the corresponding primary hydrocarbon alcohols. Examples of such reactions are esterification with acids, condensation with isocyanates, salt formation with reactive metals, and oxidation to aldehydes and acids. Because of the inductive effect of highly fluorinated alkyl
69 102 132 155-160 185-190
109 141 170 156 181 200-202
... ...
760 760 760 200 200
200
...
...
chain, fluoro alcohols are considerably more acidic than ethyl alcohol, but less acidic than phenol (dissociation constants of ethyl alcohol, 2.9 X 1O-l6; fluoro alcohols, 4 X 10-l2; phenol, 1.3 X 10-lO). The w-hydrogen in the fluoro alcohol is usually inert in most chemical reactions. I n many cases, however, it does exert a considerable effect on the physical properties of the compounds as compared to the corresponding w-trifluoro compounds. This effect appears in higher dielectric constants (72)) higher boiling points, and higher flash points. Esters of these alcohols have higher viscosity indices and lower freezing points, while maintaining the oxidative stability of the w-trifluoro types (6). Surface properties of certain derivatives have also been compared with the w-trifluoro types ( 5 ) . The fluoro alcohols can be oxidized to the corresponding wH-perfluoro acids by potassium permanganate or nitric acid. The alkali metal and ammonium salts of the C7 and higher acids exhibit strong surfactant properties which make them useful as wetting, dispersing, and emulsifying agents where a high order
Liquid Fluoro Alcohols Surface tensions and refractive indices of liquid are low but density increases with increasing fluorine content
General Formula, na
ng
dto 1.4713 1.6669 1.7501
Ionization Constant (8)
27.6 1.3210 4.6 X 10-l2 24.5 1.3178 4.5 x 10-12 23.8 1.3180 H(CF&Fz),CHsOH. 99% Minimum by vapor phase chromatography. 1 2 3
a
Surface Tension, Dynes/Cm.
VOL. 51, NO. 7
JULY 1959
829
~~~~~
of chemical stability is required. They are not attacked by conventional freeradical initiators and are valuable as dispersing agents in the aqueous polymerization of various vinyl monomers.
~
Properties of wH-Perfluoro Acids Water solubility decreases rapidly above seven carbon chain length
Other Derivatives
n
T h e reaction of a fluoro alcohol with phosphorus oxychloride or phosphorus pentoxide, followed by hydrolysis, results in a series of mono-, di-, and trifluoroalkyl phosphate esters (2):
O
c.
B.P.
134 166 106 123 152
1 2 3 4 5 6
*..
M.P., Mm. 760 760 20 20 23
...
C.
Liquid 0 34 67 108 138
Water
Solubility, % m m m
1-2
