[CONTRIBUTION FROM ~ r D~PAETMHINT n OF CHBMIBTBY, TEXIS T AUNIWMITY ~ OB IOWA]
T H E POLYMERIZATION OF HOMOLOGS OF ETEIYLENIMINE (1) GIFFIN D. JONES JuW 16, 1 9 4
&&3d
In the first paper of this series the authors reported reasons for considering the polymerization of ethylenhine (I) to be a bimolecular reaction of monomer with ethylenimmonium (and substituted ethylenimmonium) ions (11). This is is s y m b o l i d below; A may be hydrogen, boron fluoride, alkyl, etc. CHn
I
\ /" +
CHa
CHe
\+
NH-(CHaC Ha")
n-A
+
CHz
CHz \+ "(CHI
C Hz NH) n+l-A
CH2
I
I1
This is contrary to the conclusions of Kern and Brenneisen (2) who comider the isolation of low molecular weight products to indicate condensation polymerization. The isolation of dimers and trimers of typical vinyl monomers under conditions causing polymerization is so rare (3) that such isolation is commonly accepted as contraindicating an addition mechanism. An alternative conclusion (3) is that the dimerization and polymerization occur by different mechaxisms. With full appreciation of the vast differences in behavior of dimerization and polymerization, the author would like t o question both of the above conclusions and subscribe to the view previously expressed (4)that the mechanisms are the same to the extent of having a common intermediate, environmental conditions determining a t each stage which course the reaction takes. For example in the cme of isobutylene there is the common intermediate (111) (where A may be -H or -BK) if one may apply to the polymerization the mechanism of polar catalysis developed by Williams (5) and accept for the dimerization the picture of Whitmore (6). CHI
(CH&C=CHz
I
+C-cHa
I
CHs
4- BFs
H+ 4-
CHs
*
I I
-
+C-CH,BFs CHa
I
monomer
.1
-1
monomer
CHi
CHa
CHa
CHa
I I + C-CHz-C-CHnA I I I11 484
-=l
485
POLYMERIZATION OF ETHYLENIMINE HOMOLOGS
CHI^
I + C-CHZ-
I
CH3
CHa
[ (IH. -C-CH,
CHI
C Hz
C-CHz-BFs L i H 3
-
II
CH3
I
C-CH2-C-CHs CH3 I CHI
I
CH3
CH3
I I + C=CH-C-CH?
I
CH3
I
CHa
IV
With isobutylene it may not be possible to find a single set of conditions yielding both polymer and dimer, although some of the factors influencing the two reactions are known. For example, it has been pointed out (7) to the author that the lower the temperature the greater may be the stability of the intermediate (111) [and the higher homologs (IV)]toward loss of a proton (termination). This would seem to be a probable explanation for the extremely large polyisobutylenes obtained a t very low temperatures (8). With monomers having less pronounced polymerization tendencies, such as the alkylenimines, it is possible to select conditions such that polymer, dimer, and trimer can be isolated in the same experiment. The author can find no acceptable alternative to believing that these are products of a common mechanism. In the present work 2,2-dimethylethylenimine(IV) was polymerized in aqueous solution with hydrochloric acid. Contrary to the behavior of polyethylenimine, poly-:!, 2-dimethylethylenimine is soluble in ether and insoluble in water. The polymerization mixture was extracted with ether and distilled giving a low yield of three distinct intermediates and a good yield of purified waxy polymer. Nitrogen analyses and boiling points indicated the three intermediates to be a dimer (V), a hydrolyzed dimer (VI), and a trimer (VII). CHz
CHy
HOCH2 C(CH3)2NHCHgC(CH3)2"2
VI
v In assigning structures to these products consideration was given to the isolation from the sulfuric acid hydrolysis by Cairns (9) of l-amino-2-methyl-2-propanol of 2,2-dimethylethylenimine. This would suggest that a mechanistic critical point lies between the secondary imine and tertiary imine structure, since Gabriel and Ohle (10) found 1,2-~ropylenimineto be cleaved to 0-bromoisopropylamine. Preference of the primary carbon over the secondary, as in the latter case, would indicate an inversion mechanism while preference of tertiary over primary, as in the former case, mould indicate an ionization mechanism (11). Hughes and Ingold (11) have, however, demonstrated that a shift to a stronger attacking anion or donor molecule may institute bimolecular inversion with structures which undergo the ionization mechanism in the presence of less strongly nucleophilic reagents. In this connection it is to be noted that the immonium nitrogen exerts (through the carbon which is not to be severed from the nitrogen) an inductive effect favoring inversion. The two mechanisms are diagrammed in Figure 1.
486
GIFFIN D. JONES
The hydrolyzed dimer (VI) was synthesized by the reaction of p-chloro-tertbutylamine hydrochloride and 2-amino-2-methyl-1-propanol. The former was made by the action of thionyl chloride on the hydrochloride of the latter. The product of this synthesis and the hydrolyzed dimer gave identical phthalyl acetyl derivatives (VIII). This synthesis could yield either of the isomers (VIb) or (VIc) ; however, since the structure of the 2-amino-2-methyl-1-propanol is fixed, the uncertainty in this synthesis is different from the uncertainty in the structure of the hydrolyzed dimer which thus must be of the structure (VIb). The hydrolyzed dimer could have the structure (VIc) only if there were an SN1mechanism in dimerization and SN2 in hydrolysis; however, this is impossible since SN2 is favored with increasing donor or anionoid power and water is a poorer donor or base than the imine. From the compound (VIb) the dimer (Vb) was obtained by the Wenker method (12) and the oxalates found to be identical. That the imine could be prepared substantiates the structure assigned, since Adams and Cairns (13) found that l-amino-2-methyl-2-propanolcould not be converted to 2 2-dimethylethylenimine by the Wenker method. In order to confirm the structure of the hydrolyzed dimer (VIb) it was synthesized by an alternative route. Isobutylene chlorohydrin was condensed with 2-methyl-2-amino-1-propanol, yielding the amino glycol (IX). That no rearrangement of the isobutylene chlorohydrin had occurred during the reaction was indicated by the conversion of the amino glycol with acetic anhydride, hydrogen chloride, and acetyl chloride to the chlorodiacetyl derivative (X) By the method of Harvey and Caplan (14) for alkylating urea with tertiary alcohols in the presence of concentrated sulfuric acid, the amino glycol (IX) was caused to react with urea and the product hydrolyzed to (VIb), identified by comparison of the phthalyl acetyl derivatives.
Ac
c1
I
I
(CHa)z C-CH2-N-C(CHs)z
CH~OAC
X OH
I
OH
2"
I
I
t
(CH3)z CCH2 C1+ (CH3)z CCH2 OH + (CHa)2-C-CH2NHC
(CH3)z CH2 OH
IX 2"
I
T
(CH3)z C-CHzNHC(CH,)zCH2OH VIb The conclusion that aliphatic 1,2-alkylenimines tend to polymerize by the inversion mechanism is supported by rough rate comparisons made with a group of alkylenimines in the present work. It was found that 1,2-alkylenimines having a primary carbon in the imine ring polymerize about as readily as ethylenimine while the others polymerize much less easily. It is not possible to say
POLYMERIZATION OF ETHYLENIMINE HOMOLOGS
RGURE la
1
CH2 :CHa)zC/
\
cH'-- monomer
NHz
+
lt
+
:C&)z C-CHzNHz
ionization mechanim SN1
I
monomer
CHS [CHslzC-
1
NH
+
VIIS
487
488
GIFFIN D. JONES
as yet which mechanism and consequently which carbon is preferred with imines having both a secondary and a tertiary carbon in the ring. The imines used were ethylenimine (15), 1,2-propylenimine (16), 1,2-butylenimine (17), 2,2-dimethylethylenimine (9) [readily prepared by the Wenker method (12) from ethanolamine, 1-amino-2-propanol, 2-amino-1-butanol, and 2-amino-2-methy1-1-propano1, respectively], trans-2,3-butylenimine, 2,2,3-trimethylethylenimine, and 2,2-dimethyl-3-n-propylethylenimine (the last prepared FIGURE lb CHa
I
CHI 12C -
T
CH3
NH-C-CHQ-NH-
+
I
CHI
monomer, n times
\-H+
I inversion mechanisx
T
CHs II H
SN2
2
CH3
CHa
I
I I
:CHa)nC-NH-CHrC-NHz -k CH,
I
f
CH, Vb
monomer
CHz
/ \
+
t
H+ monomer
CHzOH
CHa VIb
from 2-amino-2-methyl-3-hexanol). For the preparation of 2,3-butylenimine and 2,2,3-trimethylethyleniminethe nitro alcohols, 3-nitro-2-butanol and 3nitro-3-methyl-2-butanol were prepared after the method of Hass and Vanderbilt (18) and hydrogenated according to Johnson and Degering (19) to the corresponding amino alcohols. The only 1,3-alkylenimine studied was trimethylenimine which was prepared in very poor yield by the reduction of N,N-trimethylene-p- toluenesulfonamide according to the method of Howard and Marckwald (20).
489
POLYMERIZATION OF ETHYLENIMINE HOMOLOGS
Cyclopropylamine, although not an alkylenimine, was included in the study because of the “resemblance in chemical behavior of cyclopropane and its
CH~OH
CH.2
CH,
VIb
CH,
VIC
I
phthalic anhydride
1
CHs (CHJzC-NH-CHz-C-N
I
CHzOH
I CH3
/if)
Acetic
1
anhydride [HzSOrl
0
II \/
’
0
0
0 VI11
derivatives to the corresponding olefinic compounds’’ (21). The cyclopropylamine was prepared by a Hofmann degmdation of cyclopropane carbonamide
490
GIFFIN D. JONES
following the directions of Lipp, Buchkremer, and Seeles (22) for the isolation of cyclopropylurethan. The polymerization of cyclopropylamine by boron fluoride yielded ammonia and a product low in nitrogen and was probably in part due to the formation of the readily polymerizable cyclopropene (23). The 3-amino-2-butanol was not readily separated by fractional distillation into two pure diastereoisomeric amino alcohols. The higher and more nearly constant boiling 3-amino-2-butanol was converted by the Wenker method mainly to trans-2 ,3-butylenimine, identified as the benzenesulfonimide (24). When the cis- and trans-2,3-butylenimines are available in sufficient quantity it will be interesting to compare the polymers. That from the former should be a mesopolymer of irregular structure; that from the latter, of regular structure. h good method of determining the rates of polymerization of the alkylenimines is lacking. If the polymerization is not too complete the extent of polymerization can be determined fairly accurately by evaporation, using aqueous potassium hydroxide to quench the polymerization except where polymerization was carried out a t 150" and hence could be quenched by cooling. The calibration of viscosity change is an easier method which suffers, however, from the neglecting of the effect of variation in the degree of polymerization. The change in refractive index in aqueous solution has been followed (1) with ethylenimine and 1,2propylenimine and the refractometer readings followed the same curve in the case of 2,2-dimethylethylenimine,but the data could not be calibrated in the latter case since the polymer which slowly precipitates is water-insoluble (ethersoluble). Trimethylenimine, 2 3-butylenimine7 and 2 2 ,3-trimethylethylenimine underwent no refractive index change under the same conditions. With 5 mole per cent boron trifluoride etherate, which has been used as a polymerization catalyst by Hanford and Sterenson (25), at 150" during twentyfour hours, the primary 1,2-alkylenimines were completely polymerized and triniethylenimine about three-fourths polymerized; 2,3-butylenimine was less than half polymerized as was 2,2-dimethyl-3-n-propylethylenimine.With 10 mole per cent boron trifluoride etherate a t 150" during one hundred fifty hours, trans-2 ,3-butylenimine was completely polymerized, and 2,2,3-trimethylethylenimine, 2 ,2-dimethyl-3-n-propylethylenimine7and cyclopropylamine were less than half polymerized. With 3 mole per cent alcoholic hydrogen chloride a t 150" for twenty-four hours the primary alkylenimines were completely polymerized and trans-2 ,3-butylenimines about three-fourths polymerized. The polymers obtained were probably of lorn molecular weight, being viscous liquids or gums except for poly-2 2-dimethylethylenimine which was waxy. )
)
)
EXPERIMENTAL PART
Preparation of the monomers.' The monomers used with the exception of trimethylenimine and cyclopropylamine were prepared by the Wenker (12) method with the results reported in Table I. The available amino alcohols used for the preparation of the imines were ethanolamine, 1-amino-2-propanol (isopropanolamine), 2-amino-1-butanol, and 2amino-2-methyl-1-propanol; some 2-amino-2-methyl-3-hexanol was also obtained.* 1 2
Some of the monomers were prepared by Mr. Alexander May working in this laboratory. The 2-amino-2-methyl-3-hexanol was kindly supplied by Commercial Solvents Corp.
POLYMERIZATION O F ETHYLENIMINE HOMOLOGS
49 1
For the preparation of 2,3-butylenimine and 2,2,3-trimethylethylenimine,3-nitro-2butanol and 3-nitro-3-methyl-2-butanol were prepared in ten-mole runs after the method of Hass and Vanderbilt (18) and hydrogenated3 by the directions of Johnson and Degering (19). Hydrogenation a t low pressure with platinum oxide gave higher yields (50%) than were obtained with nickel a t high pressure (30%), a considerable tar resulting (this is a combined crude yield for the 3-amino-2-butanol). 3-Nitro-2-butanol; yield 77%; b.p. 74-76" a t 3 mm.; n t 1.4420. 3-hTitro-3-methyl-2-butanol; yield75%; b.p. 7&8Ooat3mm.; n: 1.4428; n: 1.4416. Anal. Calc'd for C5HllN03: N, 10.49. Found: N, 10.52. 3-Amino-2-butanol; 116-119" a t 185 mm.; n: 1.4445; yield 16% after refractionation in 30411. Fenskc column; lower fraction 85-105" a t 185 mm.; n: 1.4425; yield 3%. 3-Amino-3-methol-2-butanol; yield 30%; 63-65' a t 15 mm.; n: 1.4434; dii 0.9153. The 3,5-dinitrobenzoate of 3-nitro-3-methyl-2-butanol was prepared and crystallized from benzene, m.p. 202-203". Anal. Calc'd for C I ~ H I ~ N N, ~ O12.84. ~: Found: N, 13.12. The hydrochloride of 3-amino-3-methyl-2-butanolmelted a t 172-174'. Anal. Calc'd for CsHlrClNO: C1, 25.29. Found: C1, 25.75. The oxalate of the 3-amino-2-butanol was prepared in alcohol and melted a t 211-212'. TABLE I ALKYLENIMINES IMINE
Ethylenimine 1,2-Propylenimine 1,2-Butylenimine trans-2,3-Butylenimine 2,2-Dimethylethylenimine 2.2,3-Trimethylethylenimine 2,2-Dimethyl-3-n-propyle thylenimine
YIELD,
"c
%
B.P.,
32 65 46 47 68 19 57
55-56 63-64 88-89 75-76 69-70 83-85 128-129
LIT.
1.4123 1.4095 1.4165 1.4070 1.4050 0.8020 1.4240
15.82 16.44 12.59 12.37
Anal. Calc'd for CIOHNNIOI: N, 10.44. Found: N, 10.51. From the lower-boiling3-amino-2-butanol, b.p./185 mm. 85-105", n: 1.4425,which was obtained impure and in the lesser amount of a combined 26% yield, an oxalate of m.p. 199-200' was obtained. Mixtures of the two oxalates gave intermediate melting points. Anal. Calc'd for CloH&208: N, 10.44. Found: N, 10.58. The acid oxalates, which were readily interconvertible with the corresponding normal oxalates, were more soluble and melted at 164-165" and 135-145", respectively. From the 3-amino-2-butanol boiling a t 116-119", 185 mm., in a 30-in. Fenske column there was obtained by the Wenker method an impure lower-boiling imine, presumably the dl2,3-butylenimine, b.p. 65-76"; n: 1.4074; 17% yield and the trans-2,3-butylenimine, b.p. 76-77'; n: 1.4105; 30% yield. The latter imine yielded the trans-2,3-butylenbenzenesulfonimide (24), m.p. 77-77.5", after immediate pressing out on clay plate and one recrystallixation from aqueous alcohol. If the Schotten-Baumann benzoylation was carried out with 10% instead of 5y0 sodium hydroxide, the product formed an oil crystallizing on dilution and melting a t 230". After the method of Adams and Leffler (26) meso-2,3-butanediol ( t e ~ h n i c a lwas ) ~ con3 The author is indebted to Dr. H. R . Snyder for carrying out some of the reductions in Organic Chemical Manufactures a t the University of Illinois. 4 Kindly supplied by Dr. G. E. Ward, Northern Regional Research Laboratory, U. S. D. A., and by the Heyden Chemical Corporation.
492
GIFFIN D. JONES
verted by hydrogen chloride to 2,3-dichlorobutane (57%) and 2,3-butylene chlorohydrin (15%); b.p./30mm. 52-54"; d? 1.0602 found; dZ51 0610 reported (27) for erythro-2,3-butylene chlorohydrin. This was converted to the oxide, b.p. 53-55'; d: 0.8008 found; & 0.8053 reported (28) for trans-2,3-butylene oxide; yield 55%. The oxide was treated with aqueous b.p. 15(r16Oo;n: 1.4435;5%yield; oxalate 214-214.5'. ammonia, yielding3-amino-2-butanol; Trimethylenimine was prepared from N , N-trimethylene-p-toluenesulfonamide5 which was reduced according to the directions of Howard and Marckwald (20) with sodium and isoamyl alcohol; yield 14%; b.p. 59.5-60.5'; n: 1.4282. Cyclopropylamine was prepared by the degradation] in the manner of Lipp, Buchkremer, and Seeles (22) of cyclopropane carbonamide6 to the urethan in 73% yield. The urethan was hydrolyzed to cyclopropylamine hydrochloride, m.p. 85-86', in a yield of 74% and the free cyclopropylamine liberated in 70% yield, b.p. 49-49.5", n: 1.4195. Isolation of intermediates in polymerization of d,d-dimethylethylenimine. 2,2-Dimethylethylenimine (42 g., 0.59 mole) freshly distilled was dissolved in 274 cc. of water, chilled to 10" and treated with 15.2 cc. of hydrochloric acid (5.121 N ) . The solution became turbid after two days a t 25" and a white, flocculent precipitate had formed after three days. This precipitate was basic, contained a trace (less than 1.001,) of chlorine, was soluble in ether and in hot alcohol, m.p. 54-56", vrei 1.073 for a 1%solution in chloroform. ilfter eight days 100 cc. of 40% sodium hydroxide solution was added to free that part of the product existing as the hydrochloride and the gummy precipitate extracted with ether. A portion of the extract, dried with magnesium sulfate, was treated with ethereal hydrogen chloride forming a white, thready precipitate which could be dried and powdered. -4nal. Calc'd for CaIf&lN: C1, 32.96. Found: C1, 33.6. The ether was distilled from the extract and the residue heated in a Claisen flask a t a bath temperature of 175" and 1mm. pressure for six hours; the distillation temperature rose gradually to 120" and then fell. The yellow residue solidified to a wax on cooling, yield 20 g.; qrei 1.085 (1% in chloroform). Anal. Calc'd for (C4HoN),: N, 19.70. Found: N, 19.70. The distillate was redistilled in a 10-cc. modified Claisen flask yielding three fractions: Fraction 1. (formula V) b.p. 67-80' a t 23 mm., 1.5 g., n: 1.4357, non-viscous; evolved nitrogen from nitrous acid. Anal. Calc'd for CsHlsN2: K, 19.70. Found: N, 20.6. Fraction 2. (formula VI) b.p. 95-100" a t 2mm., 4 g., n g 1.4516, viscous. Anal. Calc'd for CsH2oNZO: K, 17.45. Found: 17.15. Fraction 3. (formula VII) b.p. 120-140" a t 2 mm., 4 g., n: 1.4593, viscous. Anal. Calc'd for Cl2HZ7N3:N, 19.70. Found: N, 19.14. From fraction 1 was obtained an oxalate, m.p. 167-168'. Anal. Calc'd for Cl~H?oNnO4: N, 12.05. Found: N, 14.0. From fraction 2 was obtained a phthalyl acetyl derivative (XIII) after the method of Hanford and Stevensen (25), m.p. 180-18lo. -4nal. Calc'd for CzoH&205: K,7.48. Found: N, 7.93. p-Chloro-tert-butylamine hydrochloride. 2-Amino-2-methylpropanolhydrochloride (75 g . , 0.6 mole), m.p. 195-196", prepared from 2-amino-2-methylpropanol and alcoholic hydrogen chloride, was refluxed overnight with 300 cc. (500 g., 4.2 moles) of thionyl chloride. The thionyl chloride was distilled under reduced pressure and the product recrystallized from alcohol, m.p. 205-207"; yield 58 g., 65%. Anal. Calc'd for CaHllClzN:C1, 49.23. Found: C1, 48.6. Less drastic treatment of the starting material caused very incomplete chlorination. Reaction of p-chloro-tert-butylamine and 8-amino-2-methylpropanol.@-Chloro-tert-butylamine hydrochloride (54 g., 0.375 mole) was added t o 94 g. (1.05 mole) 2-amino-2-methylThe N,N-trimethylene-p-toluenesulfonamideand the cyclopropane carbonamide were prepared by Dr. G. H. Coleman and Dr. Chester M. McCloskey in Organic Chemical Manufactures at the State University of Iowa.
POLYMERIZATION OF ETHYLENIMINE HOMOLOGS
493
propanol and the viscous solution, which became somewhat warm, was heated overnight at 100'. The mixture was then dissolved in water, chilled, treated with 100 cc. of 40% sodium hydroxide solution, and extracted twice with 200 cc. of ether and twice with 200 cc. of chloroform. The extracts were dried with "Drierite", and after distillation of the solvent the residue was distilled through a 6-in., all-glass column packed with glass helices. There was recovered 40.5 g. 2-amino-2-methy1propano1, b.p./27 mm., 83-87' and obtained 29.5 g. of viscous product, b.p./18 mm. 110-130"; 50% yield. This product was redistilled yielding 12 g. of viscous liquid, b.p./l mm. 80-82", nt 1.4637, and 9 g. of viscous liquid, b.p./l mm. 90-120", n: 1.4700. From the former fraction, 2-(@-aminoisobutylamino)-2-methyl-l-propanol, was obtained a phthalyl acetyl derivative (VIII) (27) of m.p. 179-180"; mixed melting point 179-180' with the phthalyl acetyl derivative from fraction 2 (VI) of the intermediates isolated from the polymerization of 2,2-dimethylethylenimine. N - (8-aminoisobutyl) -.2,2-dimethyZethylenimine. 2- (@-.4minoisobutylamino)-2-methyl-1propanol, b.p./7 mm. 105-110° (45 g., 0.28 mole) was converted to K-(@-aminoisobutyl)-2,2dimethylethylenimine by sulfuric acid (58 g., 0.56 mole) in the Wenker method; yield 11g., 28%, b.p. 23 mm. 40-45" (in 6-in. all-glass column), n z 1.4398. The oxalate, prepared in absolute alcohol in the cold, melted a t 160-161"; mixed melting point with oxalate of fraction 1 isolated from polymerization of 2,2-dimethylethyleniminewas 163-165". Recrystallization by heating or precipitation from water yielded a product melting at 195-205". The imine reacted vigorously with alcoholic hydrogen chloride yielding a crystalline hydrochloride which was recrystallized from aqueous alcohol, m.p. above 250". Anal. Calc'd for CsHzoClzNt: C1, 32.95. Found: C1, 30.2. Attempted preparation of N-[@-(@-aminoisobutylamino)isobutyll-2,2-dimethylethylenimine. The second product from the reaction of @-chloro-tert-butylaminewith 2-amino-2-methyl-lpropanol, presumably 2-(@-aminoisobutylamino)isobutylamino-2-methyl-l-propanol,(30 g., 0.13 mole) was converted by sulfuric acid (0.40mole) to the imine by the Wenker method; yield 6.5 g. of b.p.12 mm. 115-130", n: 1.4663 and 5 g. of b.p./2 mm. 130-140", n: 1.4688. The former reacted vigorously with alcoholic hydrogen chloride, yielding a gum which was converted t o a solid by shaking with absolute ether and which softened over a wide range. Anal. Calc'd for CI~H~OCI&;J: C1, 32.95. Found: GI, 29.4. Reaction of isobutylene chlorohydrin and 2-amino-2-methyl-1 -propanol. To 2-amino-2methyl-1-propanol (445 g., 5.0 mole) refluxing in all-glass apparatus isobutylene chlorohydrin (274 g., 2.52 mole) was added dropwise. After refluxing overnight the solution was treated in the cold with excess 25% potassium hydroxide and the aqueous layer extracted with six 100-cc. portions of chloroform. The chloroform extracts were combined with the upper layer and the mixture distilled through a 6-in. all-glass heated still head packed with glass helices, yield 271 g., 6770, of 2-(@-hydroxyisobutylamino)-2-methyl-l-propanol, (IX), b.p./3 mm. 120-130'; n g 1.4580. The chlorodiacetyl derivative (X) of the above amino glycol was prepared by the reaction of acetic anhydride (51 g., 0.50 mole) with the 2-(@-hydroxyisobutylamino)-2-methyl-lpropanol (80 g . , 0.50 mole), followed by the introduction of 18 g. (0.50 mole) of hydrogen chloride and the addition of 100 g. (1.28 mole) of acetyl chloride. The product was distilled through a 6-in. all-glass still head with some decomposition, yield 47 g., 37%, b.p./7 mm. 140-150°. Anal. Calc'd for ClzH&ll\j03: C1, 13.76. Found: C1, 13.97. Attempted reaction of this product with potassium phthalimide suspended i n butyl alcohol yielded only phthalimide. Conversion of 2-(@-hydroxyisobutylamino)-~-methyl-l-propanolto 2-(@-aminoisobutylamino)-2-methyl-l-propanoZ.After the method of Harvey and Caplan (14)for the alkylation of urea with a tertiary alcohol, urea (35 g.) was added t o 130 cc. of sulfuric acid (conc'd) with mechanical stirring and cooling to keep the temperature below 30". T o the solution was added 75 g . of 2-(@-hydroxyisobutylamino)-2-methyl-l-propanol a t a rate such that the
494
GIFFIN D. JONES
temperature was kept between B25O. Near the end of the addition stirring was nearly impossible. After standing overnight the solution was poured on one liter of ice and neutralized to Congo red with 6 N sodium hydroxide. The sodium sulfate was filtered and the solution evaporated on the steam-bath with mechanical stirring and a purified air jet. The residue was filtered when nearly dry and washed with chloroform and alcohol (abs.). The combined filtrates were evaporated and the viscous residue dissolved in 200 cc. of water and heated overnight on the steam-bath with 200 cc. of 50y0 potassium hydroxide solution, an effervescence of ammonia occurring. The upper red layer was separated and the aqueous layer extracted three times with ether. The combined extracts and upper layer wcre distilled, yielding a first fraction, 19 g . , b.p./l mm. 5O-55", I L ; 1.1350, a second fraction, 4.5 g., b.p./l mni. 82-83", ng 1.4526, and a third fraction, 9 g . , b.p./9 mm. 110". n! 1.4513, this last fraction being recovered 2-(~-hydroxyisobutylamino)-2-methyl-l-propanol. From fraction 2 was obtained a phthalyl acetyl derivative after the method of Hanford and Stevenson (25) which melted a t 179-180", mixed m.p. with the phthalyl acetyl derivative of fraction 2 of the intermediates isolated from the polymerization of 2,2-dimethylethylenimine, 179-180". Tests of the polymerizability of the monomers. Evaporation of polymer solution gave a rough estimation of the concentration as indicated in the following experiment. A 4.483-g. portion of a 6.56% solution of polyethylenimine in ethylenimine, having a viscosity relative to pure ethylenimine of 1.90, wa's treated with a solution (2.257 N ) containing 0.6212 g. of potassium hydroxide, distilled to dryness and baked on a steam-bath in a modified Claisen flask connected to an aspirator. There was a 0.9236 g. residue of constant weight, a-hich would indicate an initial concentration of 6.75y0 after correction for the potassium hydroxide. The tests of Table I1 were run in sealed tubes placed inside metal tubes and immersed in a n oil-bath for the runs at 150". After the run the tubes were chilled, opened, and the contents dissolved in 20 cc. of absolute alcohol. The solutions were placed in tared Petri dishes and evaporated t o constant weight in a vacuum oven a t 10 mm. and 50". The boron trifluoride etherate was prepared according to the directions of Hennion, Hinton, and Nieuwland (29). The tests were run with 0.1-mole portions for the most part; where this was not the case the amount of catalyst was changed to keep a constant mole ratio of catalyst t o monomer in a given experiment. The weights on evaporation after polymerization were corrected for the weight of catalyst, and in the case of runs at room temperature, for the weight of potassium hydroxide added to arrest polymerization. I n the tests with cyclopropylamine, trans-2,3-butylenimine, and 2,2-dimethylethylenimine, the product was heterogeneous, having gummy precipitated polymer with a non-viscous upper layer with the first, a viscous upper layer with the second, and a white wax with the third. A considerable amount of ammonia was evolved on opening the cyclopropylamine tube and this test blew up in several earlier experiments. The product was lower in nitrogen (13.43%) than would be calculated (19.3%) by assuming all of the catalyst to be retained. Some further tests were made with cyclopropylamine sealed in 2-cc. portions in tubes with various catalyst and a t the end of the test the cyclopropylamine recovered by distillation with the yield indicated. I n the last case most of the cyclopropylamine was converted to a brown layer above the water. This was viscous, basic, and mainly undistillable; yield 68%. A chloroform solution of this product yielded no precipitate on treating with alcoholic hydrogen chloride. The residue on evaporation had qrri 1.008 (1% in water) and hence was probably not, a polymer. While 2,2-dimethylethyleniniine underwent a refractive index change in aqueous solution parallel to the changes reported (1) with ethylenimine and propylenimine, the curve could not be calibrated with the 2,2-dimethylethyleniminebecause the polymer, somewhat slow t o precipitate, was only slightly soluble in water. Trimethylenimine, 2,3-butyleni-
495
POLYMERIZATION OF ETHYLENIMINE HOMOLOGS
mine and 2,2,3-trimethylethylenimineunderwent no refractive index change under the same conditions.
5
MOLE PER
TABLE I1 POLYMERIZATION EXPERIMENTS CENT BORON TRIFLUORIDE ETHERATE, 24
I
XONOYER
E thylenimine Propylenimine 1,2-Butylenimine
10
MOLE PER CENTBORON
INITIAL WT., G .
EXTENT POLYH. APPEARANCE
4.3 5.7 7.1 7.1 7.1 7.1 4.0 1.68
complete complete complete medium medium complete low complete
TRIFLUORIDE
3.0 2,2,3-Trimethylethylenimine 2,2-Dimethyl-3-n-propylethylenimine 11.3 Cyclopropylamine 5.7 trans-2,3-Butylenimine 3.56
___
3
low medium low complete
7.4 6 .O 7.3 6.4 3.1 7.4 3.2 1.28 120
I
4.3 5.7 3.6
1 ~
i
100 100 100 75 50 100 50 75
1.084 1.134 1.115 1.075 1.045 1.103 1.035 1.100
'
HRS. AT
150"
, ~
1
~
CHCls
1
1 i
medium I complete complete 1
?re1 FOR 1 % IN
POLYM.
1.00 30 4.43 39 2.45 1 43 4.32 /complete
MOLE PER CENT ALCOHOLIC HYDROGEN CHLORIDE,
Ethylenimine Propylenimine 1,2-Butylenimine trans-2,3-Butylenimine 2,2-Dimethylethylenimine
APPROX. ERCENTAGE
?INAL U T . , G.
ETHERATE,
150"
HRS. AT
24
HRS. AT
4.5 6.0 4.0
150"
100 100 100 75 100
1.052 1.093 1.085 1.068 1.089
TABLE I11 CYCLOPROPYLAMINE EXPERIMENTS CATALYST
~
~
DURATION AND TEMPERATURE
I
Ascaridole, 0.5 re. Benzoyl peroxide, U.V.L. Boron trifluoride, 0.0287 g.
90 hrs. a t 150" 95 hrs. a t 60" 36 hrs. a t 150"
% YIELD RECOV.
MONOMER
91 53 77 82 93 18 slight
Trimethylenimine which had been converted to a syrup by heating a t 150' for 15 hrs. with boron trifluoride was low in nitrogen content and had a low viscosity; qrei 1.014, 1% in water. Anal. Calc'd for (CaHrN),: N, 24.53. Found: N, 10.03. A waxy residue from the distillation of trimethylenimine was dialyzed in a sack of non-
496
GIFFIM D. JONFS
waterproofed "Cellophane" on a shaker with water circulated by distillation. The residue on evaporation (low yield) was still low in nitrogen (14.51%). Likewise 2,2,3-trimethylethyleniminewas somewhat difficult to polymerize. A portion heated 138 hrs. at 100 with 3.84 mole per cent boron trifluoride developed a viscosity relative to the monomer of approximately 48. This may be compared to the partly polymerized 2,3-dimethylethylenimine(obtained after six days at room temperature with 10 mole per cent boron trifluoride etherate) which had a viscosity relative t o the monomer of 1.87 and was shown by evaporation t o be 32% polymerized. Another portion of 2,2,3-trimethylethylenimine heated 6 days a t 70" with 14.5 mole per cent of 2-methyl-2-aminoisobutylsulfuric acid and allowed to stand six months became about as viscous as did a n ethylenimine test with 1.8 mole per cent 6-aminoethylsulfuric acid in six days at room temperature. Some 6-chloroethylamine was polymerized by warming at 40" for three hours. The viscous mass which had a low relative viscosity (vrcl 1.006 for 1%aqueous solution) was benzoylated, yield 30% of brown powder, grel 1.033 (1% in chloroform); softening point (Dennis) 88". Anal. Calc'd for (COHONO).:N, 9.52. Found: N, 9.08. Some polymerization tests were run for the purpose of checking the effect of monomer and catalyst concentration variation. In the first group varying amounts of 3 N alcoholic hydrogen chloride were added to I-cc. portions of ethylenimine in test tubes. Some increase in viscosity was observable in the last three tubes after two days. After a week the polymerization was arrested by solution in alcohol, treatment with 5 cc. of 3 N potassium hydroxide, and evaporation in Petri dishes in a vacuum oven at 50" and 10 mm. The residue was corrected for the weight of the potassium hydroxide, 0.62 g.
CORRECTED RESIDUE
cc. HCl
0.012 .02 .03
41 53 64 71 78
0.34
.44 .53 .59 .65
.04 .05
cc. HCI
CORRECTED
0.06
.07
0.68 .76
.09
.79
.10
.84
% POLYKER
RESIDUE
.os
82 91 96 95 101
.so
When a preparative scale run was made with 200 times the amounts of one of the middle tests the heat was not dissipated and the reaction blew up. With variation in the monomer concentration also the following tests were made over two days at room temperature.
ETHYLENIXINE,
cc.
/ABSOLUTE ALCOHOL,
none 1 2 3 4 5
cc.1
% POLYY.
3 N ALC. HCl cc.
0.20 .20 .20 .20 .20 .20
,
0.667 .705 .S67 .845 .707 .321
,
40.2 42.5 52.3 50.9 42.7 19.4
Some aqueous polymerizations were run with the proportions and duration found by the refractive index method (1) t o produce quarter-life polymerization of ethylenimine.
497
POLYMERIZATION O F ETHYLENIMINE HOMOLOGS
ETHYLENMINE, cc.
well% ~~
2.50 5.00 7.50 10.00
47.5 45.0 42.5 40.0
2.5 2.5 2.5 2.5
102 150 206 252
0.22 0.42 1.38 2.65
10.5 10.1 22.2 32
1.012 1.016 1.040
A similar experiment was run with 2,2-dimethylethylenimineexcept that the solutions were made up to 50 cc. in volumetric flasks with aqueous alcohol (50% by volume) and all were interrupted after six hours. HC1 (s.121 N ) , cc.
Z,~-DIMEIHYLETHYLENIMI~,
cc .
2.50 5.00 7.50 10.00
2.5 2.5 2.5 2.5
CORRECTED RESIDUE
0.29 .43 .60 .51
I
70 POLYM.
11.5% 8.6 8.0 5.1
Ethylenimine (9.5 g., 0.221 mole) was polymerized with ,t?-aminoethyIsuIfuric acid (0.5 g., 0.0035 mole) made in absolute ether and dried. After twenty-four hours a white precipitate clung t o the walls of the vessel; most of the contents remained fluid but slowly thickened over two months to a honey-like liquid. This product was dialyzed to negligible conductivity and the concentration determined by evaporation of a sample and baking of the residue t o constant weight on a steam-bath at reduced pressure; yield 3.5 g., 37%; qrei 1.082 for 1% solution. The dialyte was evaporated to a 5 g. clear gummy residue of qrei 1.041 for 1% solution. The osmotic pressure of solutions of the dialyzed polyethylenimine was determined in a n apparatus6 similar to that used by Flory (30) except made of steel since solutions of the polymer attack brass. The glass-metal connections consisted of ground joints fixed with polyethylene glycol phthalate and metal stopcocks were used instead of needle-valves. “Cellophane”, 600 PT, non-waterproofed was used as a membrane. The values obtained a t 25.0”and the relative viscosities, all in water solution, are given below constant levels were reached in three days. A 0.1% aqueous solution of polyethylene oxide (“Carbowax 4000” Carbide and Carbon Chemical Corp.) produced a Ah of 0.50 om.
c, % 0.50 0.10 0.05
~
~
Ah,
CY.
6.53 2.65 0.43
*/C
13.05 26.5 8.62
?rei
-
1.026 1.004 -
~
More work will be required to interpret these results but the polymer is apparently of lower molecular weight than “Carbowax 4000”. 2,2-Dimethylethyleniminewas the only polyimine obtained as a solid. The author was unable to duplicate the preparation by Ulrich and Harz (31)of a solid polyethylenimine by The apparatus was constructed by Mr. J. G. Sentinella, Physics Department, State University of Iowa.
498
QIFFIN D. JONES
polymerization with 8-chloroethylamine and could not obtain a solid polyethylenimine except if i t contained a large amount of salt-forming catalyst. T o separate 5-cc. portions of ethylenimine were added 0.050 g. of 8-chloroethylamine hydrochloride, 0.050 g. of 8-chloroethylamine hydrochloride and 0.050 g. of sodium bisulfate, 0.050 g. of sodium bisulfate, 5 drops of 8-aminoethylsulfuric acid, 6 drops of 8-chloroethylamine (prepared by evaporation of a n ethereal solution under reduced pressure), and to the last, 6 drops of 6-chloroethylamine and 0.050 g. of sodium bisulfate. The tests yielded gummy polymers but no solid was formed in a month. SUMMARY
1. The polymerization of 2,2-dimethylethyleniminehas been shown to involve cleavage between the nitrogen and the primary carbon atom. The dimer and hydrolyzed dimer have been isolated and shown by synthesis to be N-(P-aminoisobutyl)-2,2-dimethylethylenimineand 2- (~-aminoisobutylamino)-2-methyl-lpropanol, respectively. 2. A group of alkylenimines was prepared and a rough comparison of their polymerization tendencies made ; only those having a three-membered ring including a t least one primary carbon polymerized readily. 3. The conclusion is drawn that the bimolecular inversion mechanism suggested in the preceding paper is applicable to homologs of ethylenimine. IOWA CITY, IA. REFERENCES (1) For the first paper in the series of which this is the second, see JONES, LANQSJOEN, NEUMANN, AND ZOMLEFER, J . Org. Chem., 9, 125 (1944). (2) KERNAND BRENNEISEN, J . prakt. Chem., 159, 193 (1941). (3) MARVEL AND HORNINQ in Gilman “Organic Chemistry”, Ed. 2, John Wiley, New York, 1943, p. 739. (4) HAMMETT “Physical Organic Chemistry”, McGraw Hill Book Co., New York, 1940, Ed. 1, p. 308. (5) WILLIAMS,J. Chem. Soc., 775 (1940). (6) WHITMORE, I d . Eng. Chem., 26,94 (1934). (7) Private Communication from Dr. C. S. Marvel. (8) THOMAS, SPARKS, FROLICA, OTTO, MUELLER-CUNRADI, J. Am. Chcm. SOC.,62, 276 (1940). (9) CAIRNS,J. A m . Chem. SOC.,63, 871 (1941). (10) GABRIELAND OHLE,Ber., 60, 815 (1917). (11) HUGHESAND INGOLD, J. Chem. SOC.,1571 (1933); 236 (1935). (12) WENKER,J. Am. Chem. Soc., 57,2328 (1935). 61,2464 (1939). (13) ADAMSAND CAIRNS,J. A m . Chem. SOC., (14) HARVEY AND CAPLAN, U.S. Patent 2,247,495 (1941). (15) GABRIEL,Ber., 21, 566 (1888). (16) HIRSCK,Ber., 23, 968 (1890). (17) Brit. Patent 460,888 (1937). (18) HASSAND VANDERBILT, Ind. Eng. Chem., 32, 34 (1940); U.S. Patent 2,139,122 (1938). (19) JOHNSON AND DEGERINQ, J . Org. Chem., 8 , 10 (1943). (20) HOWARD AND MARCKWALD, Ber., 32, 2032 (1899). (21) FUSON i n Gilman “Organic Chemistry” Ed. 2, Vol. I, John Wiley, New York, 1943, p. 101. (22) LIPP, BUCHKREMER, AND SEELES,Ann., 4 9 9 , l (1932).
POLYMERIZATION OF ETHYLENIMINE HOMOLOCB
499
(23) FREUNDLER, Bull. SOC. chim., (3) 17,614 (1897). AND ARKHANGEL’SKAYA, J. Gen. Chem. (U.S.X.R.), 7, 1914 (1937) ; (24) LIKHOSHERSTOV Chem. Abstr., 33, 519. (25) HANFORD AND STEVENSON, U.S. Patent 2,276,840 (1942). J . A m . Chem. SOC.,69, 2252 (1937). (26) ADAMSAND LEFFLER, J . A m . Chem. SOC., 63,2541 (1941). (27) LUCASAND GOULD, 60, 2396 (1936). (28) WILSONAND LUCAS,J . A m . Chem. SOC., (29) HENNION, HINTON, AND NIEUWLAND, J . A m . Chem. SOC.,66,2858 (1933). (30) FLORY, J . A m . Chent. Xoc., 66,372 (1943). AND HARZ, U.S. Patent 2,182,306 (1939). (31) ULRICH
