1968
E. E. LEWISAND M. A. NAYLOR
The product which immediately precipitated was crystallized from absolute alcohol t o a constant melting point of 128-130.5" (sintering a t 126"). Anal. Calcd. for CsHsNOl: C, 40.8; HI 6.2. Found: C, 40.5; H, 6.3. Allylamine Picrate.-Adding an ethereal solution of allylamine to a n equimolar amount of picric acid in ether resulted in the immediate precipitation of the picrate. Three crystallizations from chloroform containing a small amount of absolute alcohol furnished smoall, matted, yellow-colored crystals melting a t 141-141.5 . Anal. Calcd. for C~HloiYa07:C, 37.8; H, 3.5. Found: C, 38.0; H, 3.5. Benzenesulfonyl Derivative of Dibromopropy1amine.The bmzenesulfonyl derivative of I was formed according
Vol. 69
to the directions given for the preparation of the same derivative of 11.* Recrystallization from a e h o l yielded the alkali insoluble product VI, m. p. 89-90 Anal. Calcd. for CsH10N02SBr: C, 39.1; H, 3.7; Tu', 5.1. Found: C,39.5; H , 3 . 5 ; N,5.3.
.
Summary The crystalline precipitate formed in ethereal solution of 2,3-dibromopropylamine is 2,3-dibromopropylamine hydrobromide and not I1 as previously reported. The debromination product is allylamine and not azacyclobutadiene. CAMBRIDGE, MASSACHUSETTS RECEIVED MARCH29, 1047
[CONTRIBUTIOX FROM E I. DU PONT DE NEMOURS & COMPANY, INC]
Pyrolysis of Polytetrafluoro ethylene BY E. E. LEWISAND M. A. NAYLOR Polytetrafluoroethylene is a new polymeric ma- 760 mm. were of low molecular weight and conterial possessing unusual heat stability and chem- sisted of C2F4, C3F6 and C4Fs in varying quantiical inertness. A summary of its properties has ties depending on conditions. Since the method of been given by Renfrew and Lewis' and an at- isolation employed, i. e., Podbielniak distillation, tempt to explain these properties in terms of mo- is estimated to have accounted for 95 to 9770 of lecular structure has been given by Hanford and the products formed, it is possible, of course, that Joyce.2 small amounts of material of higher molecular Although the polymer is quite stable a t the weight and carbon tetrafluoride were formed but normal fabrication temperatures of 330 to 360°, were not detected. it does undergo degradation if it is maintained a t Experimental temperatures above 360" for extended periods of time. The extent and rate of this degradation inThe equipment used is shown in Fig. 1. The decompocrease as the temperature is raised. The materi- sition chamber consisted of a 54" length of 3/4'' iron pipe with the middle 27l/2" section heated by three electrical als obtained by cracking this polymer a t GOO to resistance Short lengths of galuanized-iron window 700" under reduced pressure are of particular in- screen werecoils. rolled into cylinders and then placed in the exit terest because of their unexpected side of the heated zone of the pipe. Ground scrap polyIt is generally believed that the products tetrafluoroethylene was fed from a hopper into the dechamber by means of a hand-operated plunger. formed by the polymerization of tetrafluoroethyl- composition decomposition products passed from the pipe through ene are straight chains having the structure aThe glass tube into two or more vacuum flasks filled with glass (-CF2-CFz-CF~-CF2-)7z terminated by as wool and placed in series. The flasks removed solid paryet unidentified end-groups. If such is the case, ticles that were being carried along in the gas stream. The one might expect the products of thermal cracking filtered g a s was compressed by means of a Model S Frigidaire refrigerating pump (driven by a l,', h. p. motor) to have structural characteristics similar to those into either of two gas cylinders. The cylinders were kept of the compounds obtained from the thermal a t approximately atmospheric pressure by cooling them in cracking of high molecular weight straight chain a methanol and Dry Ice mixture. The pressure in the hydrocarbons. This prediction would lead to the system was checked by two manometers on the vacuum side (one a t the pipe exit and one immediately before the conclusion that the low molecular weight prod- compressor) and by a compound gage on the pressure side. ucts formed should consist of straight- and The temperature of the reaction zone ivas measured by branched-chain, saturated and unsaturated com- three thermocouples brazed to the outside of the pipe. pounds along with carbon tetrafluoride. A broad During a run, the product was directed into the larger of two receivers until constant conditions of pressure and range of molecular weights in the products would the temperature had been established. The product was then be expected. diverted into the previously evacuated smaller cylinder Actually, however, the products obtained by and the analytical sample collected. For experiments low to be maintained by the Frigidairc cracking polytetrafluoroethylene a t temperatures a t pressures atooCenco Megavac pump was used. In this from 600 to 700" and a t pressures between 5 and compressor, case, the sample was collected by immersing the two traps (1) 31. h l . Renfrew and E. E. Lewis, I i d . Eng. Chcm., 38, 870 (1946). (2) W, E . Hanford and R. 31. Joyce, THISJOURNAL, 68, 2082 (1946). (3) A . F. Benning, F. B. Downing and J. D. Park, U. S . Patnit 2,394,581 (February 12, 1946). (4) E . E. Lewis, U. S. Patent 2,406,153 (August 20, 1946).
in liquid nitrogen. Pressure was controlled either by varying the rate of feed or by a throttling valve. The sample for analysis was transferred to a Podbielniak still and distilled. T P fractions were obtained boiling a t -76, -29 and -6 . These were identified as follows: C2F4.-This was the lowest boiling compound obtained from the pyrolysis. It was identified as tetrnfluoroethylene
ilug., 1947
PYROLYSIS OF POLYTETRAFLUOROETHYLENE
HOPPER,
-
1969
T H E R M O G Q E L ES
7 L -
PLJNGER
I
1
MANOMETER i
UANOMETFR'\
THREE-WAY
VENT
,--VALYE
\
,
LlQUlD N l T W G E N
JRY ICE - METHA-NQL BATHS
TRA-CS
Fig. 1.-Apparatus for the pyrolysis of polytetrsnuoroethylene. by the following properties: b. p., found -76", lit.5 -76.3"; f . p., found -142", lit.$ -142.5"; mol. wt., found 101, calcd. 100. I t was converted by direct chlorination to the 1,2-dichloride which boiled at 4', lit.6 3.8". C:jFe.-The second fraction was treated with chlorine under radiation :tt 3600 A. to yield a dichloride. The properties of the parent compound together with the dichloride are compared with the properties of hexafluoropropene and hexafluorocyclopropane and their chlorinated derivatives, 1,2-t~ichlorohexafluoropropaneand 1,3-dichlorohexafluoropi-opane, in Table I . TABLEI PHYSICAL COXSTANTS Boiling poi tit,
"C.
C1F6 fraction Hexafluoropropenc HexafluorocS clopropane CIFfi chlorinatlim product 1.2-Dichlorotiexafluoropropane 1 3-Dichlcmrhrx;rtlui ,ru,"",'
