REACTIONS OF ALPHA-OLEFINS E, CLIPP INGE R
,
California Research Cork., Richmond, Calif.
The reactions of a wide molecular weight range of a-olefins are reviewed and divided into two classes. Class I reactions are not affected b y increased chain length of a-olefins. The high solubility of the reagents involved allows the olefin itself to be the medium for the 10 reactions listed. Experimental studies on the free-radical addition of HBr to a-olefins are described as an example of this class. Class II reactions show a marked decrease in reaction rate or yield with increased chain length of a-olefins. In this case, the reagents involved are not readily soluble in a-olefins, especially olefins of higher molecular weight. For this class, yield and rate optimization siudies of the free radical NH4HS03and the ionic addition of H&04 to a-olefins are reported. The isomer distribution of the product alcohols from addition of H2S04 to dodecene i s reported in detail.
HE RECENTLY ASSOUNCED commercial availability of lowTcost a-olefins from C ; through (220 makes a review of their reactions timely. Elementary organic textbooks usually discuss the reactions of a-olefins through 1-pentene. It is apparently assumed that the high molecular weight olefins will react with equal facility, but reaction conditions used for the lower molecular weight a-olefins often cannot be extrapolated to higher molecular weight olefins. The reactions of aolefins are examined here by dividing them into two classes. I n Class I, the reaction medium is organic in nature, and the reaction conditions are little affected by changing from low to high molecular weight a-olefins. An example of this type is the free-radical addition of HBr to a-olefins. The second class broadly involves reagents soluble only in water reacting with a-olefins. These reactions are very much slowed down or even prevented as the chain length of the a-olefin approaches 20 carbon atoms. Examples of Class I1 are the free-radical addition of bisulfite to a-olefins to form primary alkylsulfonates and the ionic addition of H2S04 to a-olefins to form secondary sulfates. The example reactions listed above are reported in some detail. Improved synthetic procedures are described for extending these three reactions to higher molecular weight olefins. T h e remaining reactions have been classified with the aid of published literature and simple experiments carried out in these laboratories. Since no novel approaches were used in extending some of these known reactions to higher molecular weight olefins, experimental details are omitted.
Experimental
HBr Additions. Only a-olefins containing 0.05 + 0.02 mole 70 peroxide by iodimetry were used for the comparisons here. If larger amounts of peroxide are used, the effect of changing reaction conditions is minimized. T h e olefin was charged to a three-necked flask equipped with stirrer, condenser? and fritted-disk gas inlet tube. T h e flask was immersed in a constant temperature bath, and the HBr gas was
charged through a rotameter. Completion of the reaction was indicated by a rapid increase in the rate of exit gas flow, either through a rotameter or by visible fumes. The composition of the product \vas determined by bromine number and gas chromatography. Secondary dodecyl bromides and higher analogs are prone to eliminate HBr during gas chromatography, but primary bromides are stable. Small amounts of internal bromides are formed from the 1 to 57, internal olefins which normally contaminate a-olefins, but these are not derived from a-olefins. Bisulfite Additions. I n a typical reaction, 1.1 moles of a 5M solution of N H 4 H S 0 3 containing 10 vol. yo concentrated KHdOH was added all a t once or dropwise over a 2-hour period to a refluxing solution of 1 mole of a-olefin in 2 volumes of 507, aqueous ethyl alcohol. The reaction was carried out in a five-necked flask equipped with stirrer, addition funnel, reflux condenser, and p H electrodes. T h e reaction was followed by quaternary ammonium chloride (Hyamine) titration ( 9 ) , iodimetric determination of bisulfite, and p H monitoring. Initiators, such as tert-butyl perbenzoate, 0.1 mole %, were added a t the beginning or incrementally during the reaction for initiators of short half life. Experimental details have been reported (2). a-Olefin Sulfations. A typical reaction involved the dropwise addition of 0.15 mole of 98Y0 H 2 S 0 4over a maximum of 10 minutes to 0.10 mole of 1-dodecene in a n equal volume of n-pentane. The reaction flask was equipped with stirrer, addition funnel. and thermometer and immersed in a bath 15' to 20' C . lower than the desired reaction temperature. The addition of acid was started as the mixture reached the reaction temperature, and the addition rate was controlled to give the desired temperature. The reaction mixture was poured on ice, and the flask was washed with a n ice water mixture. The total free acid of the mixture was determined, and additional analyses were obtained, as shown in Figure 1. The dialkyl sulfate consumed 1 equivalent of X a O H and formed 1 equivalent each of detergent and alcohol during hydrolysis a t p H 8. The product sulfates were acid-hydrolyzed, and the resulting alcohols were identified by gas chromatography on a silicone-firebrick column. When less than a mole of acid was used, a trace of free alcohol was in equilibrium with the species shobvn in Figure 2. Three known secondary dodecanols were prepared for primary standards by lithium aluminum hydride reduction of the commercially available (Gallard Schlesinger, Inc.) 2-, 3-, and 4-dodecanones. VOL. 3
NO. 1 M A R C H 1 9 6 4
3
1-0lef in
Ice
Results and Discussion
Conc.H,SO,
Water Acid Layer (30-70% HnSO, Containing No Detergent)
W i t h Pentane PIUS About 10%
Alcohol
oil
Aqueous Layer
I
Warmed (80”C., 30 Min.) at pH 7-10 to Determine Dialkyl Sulfate
.
Secondary Sulfate Detergent
Figure 1.
Elemental Analysis Suggests Ether
/
I
Bromine No.
Infrared Analysis (3680 ern? 1 for Alcohol Laboratory procedure for studying sulfation
Class I. I n Table I a large number of reactions of Class I are listed. This list is not exhaustive. In the first seven reactions, the a-olefin itself is the solvent. I n these reactions, increasing the chain length of the a-olefin from C S to CIS results in only a small decrease or no change in reaction rate. I n alkylation reactions, where benzene or phenol is the solvent, the higher molecular weight olefins show a slightly lower reactivity; but since the reactions are very fast, the effect is not important. The trifluoroperacetic acid epoxidation of a-olefins, reported by Emmons (5) and used analytically by Hawthorne (a), is essentially instantaneous, so that no molecular weight effect is apparent. In earlier work by Swern (27) with peracetic acid, the same products were formed a t a rate almost insensitive to chain length of a-olefins. This contrasts with glycol formation by oxidation with aqueous K M n 0 4 where increasing chain length of a-olefin gives a very rapid drop in reaction rate. T h e esterification of a range of a-olefins with primary alkyl o-phthalates is a very recently reported case of insensitivity to chain length of olefin (79). HBR ADDITION. The free-radical addition of gaseous HBr to a number of a-olefins was examined as a n example of Class I. The results are outlined in Table 11. There was no observable decrease in rate of reaction or yield of alkyl bromide with increasing chain length of a-olefin. The only effect was
Table 1.
Class I-Reactions Insensitive to a-Olefln Chain length Reaction Ref. Peroxide
R-CH=CHz
+ HBr
R-CHzCHz
+ HIS
L R-CHZ-CHzBr
(23)
+
Peroxide
LR-CHz-CHr-SH
(R-CH2-CHz)z R-CH=CHz
+ CHaCOSH
Pcroxide
-
__t
R-CH~CHZ-SCOCH~
R--CH=CHz
+ R’CHO + Brz
R-CH=CHz
+ HC1
R-CH=CHz 80
R-CH=CHt
(70,78)
S
(3,4)
Pcroxide
R-CHs-CH-CO-R’
( 72, 75)
L R-CHBr-CHZBr
(3,23)
R-CHC1-CHJ
AlRa
+R-C-R’
+
(3,23)
Polymers
(3,25)
II
CHz R-CHzCHz
+ ,0H
R-CH=CHz
f ,0OH
AlCla
L R’--CH@-R’’
( 77)
AlCla A
R ’-CH( C6Ha-OH)-R
R-CHzCHz
8 + FaC-C-OOH R-CH-CHQ
(3,5)
0
Figure 2. 4
Sulfation of dodecene with
96% HzSOaa t 0” C-
I h E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
\
OH
(3)
-+ R-CHOH-CHzOH
‘0’
0.50 1.00 1.50 MOLE R A T I O H z S 0 4 / 0 L E F I N
’’
‘OR
’I
Table II.
Effect of a-Olefin Chain length on Primary n-Alkyl Bromide Formation"
Reaction Time, Product Iir Prim., % Sec., % Prim./sec. Olefin 2.0 85 15 5.5 1-Hexene 1-0ctene 0.5 87 13 6.7 9 10.2 1-Decene 0.5 91 5.5 17.3 1-Hexadecene 1 .0 94.5 a Gaseous H B r added at about 200 cc. per minute per mole of olefin, 20" C., no solnent in stirred three-necked flask. Ol&s contained 0.0~77~ peroxides (determined by iodimetry).
.
Table 111.
Temp., O
Product
c.
Prim.,
-3O
c.
set., %
Prim / s e d .
Contains one
Class Il-Reactions Sensitive to a-Olefin Chain length
Reaction
Ref.
Peroxide
R-CH=CHz
f HSOI-
R-CH=CHz
+ HzSOn
R-CHz-CH2-SO3-
A
(2, 6)
R'-CH-R"
(1, 73)
I I
0
SOiH
+ KMn04 ---+
R-CH=CH:!
R-CHOH-CHzOH
+ HzOz
R-CH=CHz
R-CHOH-CH20H
(22)
PdClz
+ [O]
R-CH=CHz
+ CO 4- Hz ------+
L R-CQ-CHi
(20)
CO(CO)6
R-CHCH3-CHzOH R-CHz-CH2-CH2OH
Table V.
(3)
___f
R-CEI=CH,
As indicated by the last entry in Table 111, dilution with pentane-a technique which has been used by other workers (23)-gave a n even higher proportion of primary bromide. With 1-decene and higher olefins diluted with pentane and ' C. or lower, no measurable amounts of 2-bromo reacted a t 0 compounds were fouiid. Thus, less than 2% ionic HBr addition accompanies radical HBr addition to a-olefins of high molecular weight, including various mixtures of a-olefins in the C ~toOC z orange. Class 11. T h e reactions of Class 11, which are more difficult with higher molecular weight olefins, are shown in Table IV. The free-radical addition of HS03- to a-olefins is analogous to the HBr addition. However, since the inorganic bisulfite salts are insoluble in a-olefins and the long chain a-olefins are insoluble in water, the reaction is increasingly difficult as molecular weight of olefin is increased (6). I n the case of direct sulfation of a-olefins, the 807, H Z S O ~ effective with I-hexene (7) was completely ineffective with 1hexadccene (73). This solubility effect applies to glycol formation with aqueous K M n 0 4 or H202. The last two reactions, PdC12 oxidation and the oxo process, are somewhat different. The chemical reactivity of the additional methylene groups in the larger molecules lowers yields by side reactions. This effect is added to a decreased reactivity because of increased chain length. For example, a t 20' C. the PdC12-catalyzed oxidation of propylene gave a 90% yield of acetone, while under the same conditions, 1-decene gave only a 3070 >-ieldof 2-decanone ( 2 4 ) .
70
a Conditions same as Table 11, except temperature. volume of pentane solvent.
Table IV.
a greater preference for the free-radical addition, as shown by the increasing amount of 1-bromoalkane formed. Previous reports (77, 74, 76) of decreasing reaction rates and yields with increasing chain length of a-olefin can be explained by the low solubility of the initiator, ascaridol, in the higher molecular weight olefins. This exceedingly low solubility of initiator in olefins such as 1-hexadecene and 1-octadecene was observed with lauroyl peroxide, benzoyl peroxide, and azobis(isobutyronitrile). LYith soluble peroxides or a trace of air or bromine, the free-radical reaction proceeded better in hexadecene where the nonpolar medium virtually eliminated competition from the ionic addition to form the 2-bromo derivative. The formation of the 1-bromo derivative was so strongly favored with the high molecular weight a-olefins that the effect of temperature was studied with 1-hexene. I n this case, the ratio of products could be more accurately determined. Table I11 shows that the formation of the free-radical product was much preferred a t low temperature. This is a consequence of the greater temperature sensitivity of the ionic addition reaction, since the rates of radical additions estimated from the rate of HBr take-up were essentially constant from 43' to
Effect of Temperature on I-Bromohexane Formationa
+
( 3 , 7, 24)
Effect of a-Olefin Chain length on NaHS03 Addition Rate"
50y0 MeOH refluxing at approximately 7.5' C. Olejin 76 ReactionlHr. 1-hexeneb -20 1-octene 8 1-dodecene 0.4 I-hexadecene
