Patented Aus. 24, 1948

2,447,717

UNITED STATES PATENT OFFICE
FLUORINATION OF ORGANIC COMPOUNDS

Joseph H. Sfmons, State College, Pa., ~dsnor to
Minnesota Mining & Manuh~cturing ~a~mp~ny,
St. Paul, Minn., a eorpol~tion of Deh~ware
No Drawinz. AppliestI0n ]Dec,ember ~, 1948,
Serial No. 714,918
S ~]ahus,

1
This applieztion is a contlnuation-in-par~ o!
eopending application Ser. No. 562,5~0, ~d
November ~, 1944, now abandoned.
This ~nven~on rela~es to a method of ~rec~]y
~uo~natl~ organic com~s by reaction
el~menta~ fluorine in a liq~d solvent diluent.
The fluorination of orga~c compo~ds in an
inert liquid v~hicle by means of e]ementa~
fluorine h~ ~rcviouslY been ~ropesed. Sec the
Calco~ and Bcnn~ng Patent No. ~,013.030,
Se~t. 3, 1935, w~[ch mentions anhydrous ]i~uld
hydrogen fluoride, fluorsulfonic acid, and fluo~
rinated hydrocarbons as suitable. ~ese are
r~pre~enta~ive of acidic and neutral liq~ds.
I have found that p~idine, which is readily
available at a reasonable cost, h~ marked
vantages owr ~he acidic and n~ut~l liquids
~o~ly proposed. ~ridine is basic.
Elementa~ fluo~ne ~ the most chemically
~ctive element known. ~uorinatlon Is somewhat
sIml]ar to oxi~tlon, but is an even stronger
~ction. ~uorlne reacts ~olentl~ with most
organic compounds, even a~ reduced temperatures, causing a dest~ctive decomposRion or
degradation, ~less the reaction is controlled.
Obviously a ~i~uid cannot be used as a diluent
vehicle, tn which the orga~c compound to be
fluo~nated is disgolved, if the vehicle is itself
unfavorably reactive to the clemently fluoEne.
I~ would natur~ly be supposed that p~ldine
wo~d reac~ v~o]cntl~ wi~h fluorine, as d~es
benzene.
~ have discovered, contm~ to execration, that
pyrid~e has ~It~le reactlvi~y to fluo~ne at temperatures below 0~ C. and h~ other prope~ies
~ch mak~ i~ ~gh]y suitable f~r use as ~ fluorination ’diluent.
~en elementa~ fluc~ne [s in~uced into
pyr~Inc a~ r~duced tom,futures, a molecular
c0mpl~ is fo~ed, wherein fluorine atoms are
loosely held ~ the ~y~dine molecules, and this
complex can act ~ a fluo~ating agent. ~e
complex tra~fers fluorine to the orga~c compound solute ~o ~ to ca~e fluo~na~on th~eo1
in a moderate an~ controlled fashion w~ch
~voids the ~olen~ and dest~ctive or degrad~tive
action characteristic of direct fluo~tion. ~e
effec~ Is ~
different from tha~ resulting whcn
fluorine is dissolved as a simple solution In an
ine~ solvent vehicle which does no~ form
complex. Moreover, the py~e absor~ relativel~ much larger quantities of fluorine t~n do
solvents w~ch do not form such a complex. A
f~ther adv~tage of p~ i~ that it ~ capable
of a~rbi~e small ~o~ts of hy~ogen

which may be evolved in the fluorination process,
without the vehicle being rendered acidic, owing
to the basic nature of pyridine. It has been found
advantageous tv maintain a basic -~ehicle as such
vehicle ls more favorable to the desired fluo5
rination reaction In many cases, Pyridine is an
excellent solvent, a large number of organic coml~unds being highly soluble therein.
PYridine can react with fluorine to form a
10 fluorinated pyrldlne, such as fluoropyridine
(wherein a fluorine atom replaces a hydrogen
atom and is directly bonded to a carbon atom by
a covalent bond), as distinguished from the
di~ive complex previously mentioned. However,
15 the fluorinated pyridine thus produced ls itself a
highly stable and insert solvent diluent material.
The fluorinated pyridtne is basic, forms addition
complexes with fluorine, and functions similarly
to pyrldine. Hence the effect of fluorination of
20 the pyrldine solvent is not to decrease the
molecular ratio of the inert fluorine-transferring
solvent relative to the organic solute being fluorinated, but merely to consume some of the
fluorine, making it unavailable for fluorination
25 of the organic solute. ¯
At reduced temperatures, below 0° C., the rate
of fluorination of the pyridine solvent diluent
employed in the process is quite slow, so that for
practical purPoses the diluent remains essentially
30 a pyridlne solvent and can be recovered as such
with little loss.
Even at higher temperatures, the rake of fluorination of the pyridln~ will be slow when the
solvent contains an organic compound solute
35 which is readily fluorinated. In such case the
tendency is for the fluorine atoms to fluorinate
the solute as against fluorinating the pyridine.
Since fluorinated pyridine is itself an effective
Inert solvent diluent, it can be recovered and
40 used as the diluent in performing the process.
upon other occasions. The invention embraces
the use of fluorinated pyridine asan inert solvent
diluent, and in some cases it may be desired to
employ it exclusively, without making use cf
45 pyrldine.
Thus the invention is not restricted to the use
of stmpl~ pyridine, but includes pyridine derivatives which likewise form addition complexes
with fluorine but are relatively insert to fluorina50 tion (i. e. valence bonding of fluorine) when
employed as solvent dlluents for fluorlnatoble
organic compound solutes. A further example
methyl pyrldine. Other compounds COnt~tnin~
the pyridine ring may be employed as equlvalentz,
55 such as quinoline; and other _~dne ring ccm~

STATE 07524645

1005.0001

 3
pounds containing more than one nitrogen atom
in the nucleus, such as diazines.
The reaction vessel may be of copper or silver
construction to render it corrosion-~esistant, pro*
vlded with a cooling Jacket for temperature control, and with mechanical stirring means. The
fluorine gas stream preferably enters into the
vessel below the liqUid surface and in the form
of small well-dispersed bubbles. Inlet and outlet ports may be provided for continuous operation. Where the reaction product is removable
as a vapor, further additions of the organic reactant may be made from time to time, or continuously, without further addition of solvent
diluent. A reflux condenser may be provided.
The fluorine gas may" be diluted with an inert
gas, such as nitrogen, in order to retard the reaction and permit of better control of heat in the
reaction vessel.
A catalyst may be employed but, in general,
¯ there is no need for catalytic assistance in view of
the fluorination activity.
~’he reaction of pyridine and fluorine is flinstrated by an experiment in which pyridine d~ssolved in 2-fluoropyridlne was treated at 0° C. for
four hours with fluorine gas diluted with nitrogen, resulting in the conversion of 40% of the
~yridine into fluoropyridlne. In this case the
Euoropyridine served a~ an inert solvent diluent.
The absence of a different fluorinatable organic
solute to preferentially react with fluorine explains why the pyridtne was fluorinated to this
extent. When such a fluorinatab]e organic solute is ~resent, the rate of fluorination of pyridine
is made much slower, so that it is possible for the
pyridine to behave ~s a highly inert (non-rea~tire) diluent.
The following examples further serve to illustrate the invention. All parts are by weight,
ccpt as noted.
A reaction vessel was charged with 19 parts of
toluene dissolved in 79 parts of l~ridine. Fluorine gas diluted with nitrogen (1:25 ratio) was
passed through the solution, the temperature being about m20° C. After purfflcation and distillation of the resulting reaction mixture, two fluorinated tohienes were obtained. One di~tilled at
100-110° C. at a pressure of 19-0 ram., was more
dense than water, and contained by analysis
46.4% fluorine. The other bored at 93-103" C. at
atmospheric pressure and contained 18-20% fluorine;
~luorlne diluted with nitrogen was
through a solution of 30 parts acetophenone in 79
parts pyrldine at a temperature of --25 to --40~ C.,
resulting In fluorination of the acotophenone and
the production of difluoroacetophenone.

A solution of 90 co. of dry, refractionated benzene (B. P. 80° C.) in 160 co. of dry, refractionated
pyridine (B. P. 115-116° C.), was treated with
0.75 reel of fluorine, which was diluted wi~h nitrogen in a l:10 ratio. The nitrogen had been
treated with alkaline pyrogailol to remove any
o~Tgen and then dried with phosphorous pentoxide. The reaction temperature was --15" C.
The reaction proceeded smoothly. White fumes
were evolved and the solution became dark and
somewhat viscous.
The reaction products were poured onto icecold dilute hydrochloric acid and the resUlting

4
black slurry was ether-extracted. The ether solution was separated, washed with water, dried
over solid NaOH, and fractionated through a
small five-plate column. Cuts boiling from 8086° C., t~talling 23 grams, were refraction~ted
through a small metal-packed column having an
estimated 30 theoretical plates. Decailn was
u~ed to back the distillation. The follow~ng fractions were obtained:
lO
B.P.

Cut

(co.)

.................................

15

2 ......... : ....................... l
3 .................................

Weight

Refractive
Inde~

68-79

79-800 l

1.~
13.

80-820

!.49~0
I. 49~1
1.4921
1.4753

Cut 5 had a molecular weight (Dumas gas den20 sity method) of 95.6. It was separated by low
temperature filtration through a slntored glass
disk, the lower melting fluorobenzene (M. P.
--42° C.) being thus sevarated from the l~gher
melting benzene (M. P. 50 C.). In order to ob25 tain a pure sample of fluorobenzene, only a 0.2
gram sample was collected in the first fraction.
This sample had a melting range of --46 to --42°
C.; a refractive index of 1.4698; and a fluorine
content of 18.6% as determined by Parr bomb fu30 sion and titration of the resultant fluoride ion
content with standard thorium nitrate. The theoretical value for fluorobenzene (C~H~F) is
19.7 %; and the reported refractive index value is
1.4684.
3~
The residues from the first fractionatlon were
distilled in a simple distilling flask, and the following, cuts were obtained:

A black heavy residue remained as a pot residue.
In this experiment only a sma!l amount of fluorinated pyridine was formed, demonstrating the
preferential fluorination of the benzene.
Exampl~ ~
A glass reaction vessel was filled with 65 grams
of glacial acetic acid and 169 grams of dry fractlonated pyridlne. A dry, oxygen-free, fluorine
and nitrogen mixture (1:10 ratio) was introduced
through a copper tube at the rate of 0.1 reel of
fluorine per hour, for a total of 11.5 hours. The
reaction vessel was kept at --10 to --25° C. The
reaction proceeded smoothly, with the evolution
of white fumes.
Products containing combined fluorine were
obtained. It appears probable that some fluoroacetic acid was produced.
Example 5
Fluorine gas was passed into a 10% solution
of benzene in. 2-fluoropyrldine, at a temperature
of 0° C. A solid reaction product was obtained
which, after removal of fluoropyrldine, wa~ found
to contain aly~roximately 20% fluorine by weight.

A10% solution of butyric acid in 2-fluoropyrldine was treated with fluorine ate° ~. Products
containing combined fluorine were obtained, and

STATE 07524646

1005.0002

 9,447,717

6
substantially inert to the fluorine but form~ a
molecular complex therewith acting as a fluorinating agent for the dissolved organic compound
to I)roduce fluorination thereof in a ~nooth nonAcetic acid dissolved in 2-fluoropy£1di~e was
treated with ~luor~ne at 0° C. The reaction pro- 5 violent manner, and recovering a fluorinated
product of said organic compound.
ceeded smoothly, without explosion. The prod8. In a process of producing organic fluorine
ucts were not analyzed.
compounds, introducing elementary fluorine into
Having described various embodiments of the
a liquid mixture essentially comprising fluoropyriinvention, for purposes of ~]ustratlon rat~er
10 dine and an added organic compound solute
than limitation, what I claim is as follows:
which is highly reactive to fluorine, the mixture
1. In a process of producing organic fluorine
being maintained at a temperature such that
compounds, the steps which comprise reacting
the fluoropyridine serves as a liquid solvent dilufluorine with a fluorlnatable organic compound
ent which is substantially inert to the fluorine
solute in a substantially inert liquid solvent diluforms a molecular complex therewith acting
ent of the class consisting of pyridine and fluori- 1~ but
as a fluorinating agent for the dissolved organic
nated py~ldine, and recovering a fluorinated
compound to produce fluorination thereof in a
product of said solute.
smooth non-violent manner, and recovering a
2. A method according to claim 1, wherein a
fluorinated product oi said organic compound.
reducedtemperature l~ maintained not exceeding
JOSEPH H. SIMONS.
about 0° C.
& A method according to claim 1, wherein said
REFERI~NCES CITED
organic compoUnd is a hydrocarbon.

i~ appears PrObable that some fluorobutyric acid
was produced.

4. A method according to claim 1. wherein said
organic compound is an aromatic hydrocarbon.
5. A method according to claim 1, wherein said
organic compound is an acid.
6. A method according to claim 1, wherein said
organic compound is acetic acid.
7. Tn a process o~ producing organic fluorine
compounds, introducing elementa~j fluorine into
a liquid mixture ea~entially compr~ing pyridine
and an added organic compound solute which
~s highly reactive to fluorine, the mixture being
maintained at a temperature such that the pyridine sc~ves as a liquid solvent diluent which is

The following references are of record in
file of thls patent:
T~NX’J.’,~J STATES PATENTS
Date
Name
Calcott et al ......... Sept. 3~ 1935
Daudt et al .......... Sept. 3, ~935

Number
2,013,030
2,013,035

FOREIGN PATENTS
Number
786,12~

Country
Date
France ............. JUne 3~ 1955

STATE 07524647

1005.0003