US2296614A - Liquid phase halo-substitution of partially halogenated unsaturated organic compounds - Google Patents

Description

Patented Septo 252, i942 memo rnesa HALO-SUBSTI'EIUTIIQN F PARTIALLY HALOGENATED UNSATWAT- ED ORGANIC COMPOUNDS No Drawing.

Application centerit, rose, Serial No. 299,286

6 Claims. (on. etc- 6st) The invention relates to a processior effecting the halogenation, via substitution, of partially halogenated, unsaturated organic compounds, and more particularly pertains to a practical and economical process for halogenating, via allylic substitution, a partially halogenated organic compound of the class consisting of unsaturated hydrocarbons containing an olefinic have one or more halogen atoms attached thereto.

In one of its embodiments, the invention pertains to a novel process for halogenating by allylic substitution a partially halogenated, organic compound having a general formula R. R4 Rr-( JC=( IRt wherein .1: represents a halogen atom, while R1 R each represents a hydrogen atom, an allgvl, aryl or aralkyl radical. As stated above, in cases where B2 and Rs comprise a hydrocarbon radical, these radicals may contain a chlorine atom. In iact, the other three radicals may also be chlorine -containing alkyl, aryl and/or aralkyl radicals, all of them being in nonvicinal position with respect to the halogen atom z or the secondary carbon atom of the abovepresented formula. As will be pointed out hereinbelow, it is preferable to employ as a starting material a compound of the above formula, in which one of the Rs on the carbon in' allylic position is a hydrogen atom. However, the invention is not limited to such partially halogenated compounds, since the hydrogen atom which is removed from the organic compound during the halo-substitution step may be in some other position.

In one of its most specific embodiments, the invention includes a novel, practical and economical process for the allylic halo-substitution of Z-chlor-butene-Z, and the invention also pertains to a certain novel compound derived therefrom.

It is known that partially halogenated, unsaturated organic compounds containing an olefinic linkage between two non-tertiary carbon atoms of aliphatic character, at least one of which is of secondary character, said organic compounds having a halogen atom attached to the unsaturated carbon atom of such secondary character, as well as unsaturated organic compounds of the above class, but containing one or more halogen atoms attached to carbon atoms in nonvicinal position to the carbon atom having the first mentioned halogen-atom attached thereto, may be further halogenated by reaction with a halogen such as chlorine or bromine. This reaction is either via substitution or by addition, or both by addition and substitution, depending upon the conditions of operation. Thus, as far back as 1871, Friedel and Silva (J ahresberichte uber die'Fortschritte der Chemie, page 405), studying the chlorination oi 2-chlor-propene found that in the absence of light, substitution of chlorine occurred with the formation of 2,3- dichlor-propene-l. However, when the reaction was efiected under th influence of light, the

product predominated in the halogen addition product, 1,2,2-trichlor-propane. In both cases, the reaction was efiected at low temperatures (about 0 C.) and in the liquid phase. efiected in the vapor phase at elevated temperatures, the reaction products predominate in unsaturated poly-chlor-substituted compounds. For example, vapor phase chlorination of 2- chlor-butene-2 at temperatures of about 250 C. produced predominantly the dichlor-butenes.

The reaction between a halogen such as chlorine, and a. partially halogenated, unsaturated organic compound of the above-defined type is very slow, even when efiected in the liquid phase, as compared to liquid phase halogenation of normal secondary olefins, when the two products are reacted under similar operating conditions. On the other hand, the halogenation reaction of the defined partially halogenated unsaturated organic compounds is considerably accelerated by the influence of light or when realized with relatively high halogen concentrations. However, both of these methods forincreasing the reaction rate afiect or increase the formation of products of halogen addition in preference to halo-substitution products. Therefore, these processes are of little or no value when it is desired to obtain products of halo-substitution by subjecting the aforementioned partially halogenated unsaturated organic compounds to the action of a halogen such as chlorine or bromine.

It is, therefore, one of the objects of the present invention to provide a process for the efli= When " cient and economical halogenation, via allylic substitution, of partially halogenated, unsaturated organic compounds. A further object is to provide a process whereby partially halogenated, unsaturated organic compounds of the class of unsaturated hydrocarbons containing an oleflnic linkagebetween two non-tertiary carbon atoms of an aliphatic character, one of which is of secondary character, and a halogen atom tion of halo-substituted products in preference to products of halogen addition.

I have discoveredth'at the above and other objects may be obtained by effecting the reaction in the presence of oxygen or of an oxygen-containing gas. Morespecifically stated, the invention resides in a process for halogenating a partially halogenated, unsaturated organic compound of character.

the type of an unsaturated hydrocarbon containing an oleflnic linkage between two non-tertiary carbon atoms of aliphatic character, at least one of which is of secondary character, said hydrocarbon containing a halogen atom attached to an unsaturated .carbon atom of secondary character, this process comprising subjecting such organic compounds in the liquid phase and at moderate or even subatmospheric temperatures to the action of a halogen such as chlorine or bromine, in the presence of oxygen or of an oxygen-containing gas, whereby there is eifected an allylic halo-substitution in preference to the formation of products of halogen addition.- The invention includes the realization of the abovedefined liquid phase halo-substitution, both in the dark and under the influence of light. as well as in the presence of halogen in concentrations which would normally favor halogen addition but for the presence of the aforementioned oxygen or oxygen-containing gas.

Representative halogenated, unsaturated organic compounds which may be further halogenated, via allylic halo-substitution, in accordance with the process of the present invention, include unsaturated, halogenated hydrocarbons of secondary character, of the type of 2-chlorpropene-1, 2-brom-propene-I, 2-chlor-butene-l, 2 chlor butene- 2, 2 brom-butene-l, 2-brombutene 2, 1,3 dichlor-butene-2, 1,3-dichlor-butene-3, 2-chlor 3-methyl butene-l, 2-chlor-pentene 1, 2 chlor pentene-2, 3-chlor-pentene-2, 1,3-dichlor-pentene-2, 2,4-dichlor-pentene-3, and

' the like, and their homologues and analogues. It

is to be noted that in all of the above partially halogenated, unsaturated organic compounds, a halogen atom is attached to anunsaturated carbon of secondary character. As to the unsaturated compounds having more than'one halogen atom in the molecule, the second halogen atom is attached to a carbon atom which is not in vicinal position with respect to the unsaturated carbon atom carrying the first mentioned halogen atom. As will be shown hereinbelow, the presence of oxygen during the-liquid phase halogenation of the above-defined class of partially halogenated,

unsaturated organic compounds permits halo- 'genation. via allylic substitution, under operating conditions, such as influence of light and/or excessive halogen concentrations which would have caused the halogen addition but for the presence of said oxygen. The present invention does not extend to the halogenation of the above class of partially halogenated, unsaturated compounds in the vapor phase, and at elevated temperatures. since the predominant reaction is that of halogen substitution into the allyl position even in the absence of the oxygen. Furthermore, invention does not extend to unsaturated, organic compounds wherein the halogen atom is attached to a carbonv atom of primary character, nor to partially halogenated unsaturated organic compounds' containing an oleflnic linkage between two carbon atoms one of which is of a tertiary saturated compounds wherein the halogensare attached .to vicinal carbon atoms are not within the scope of the present invention since, as will as the mono-chlor and mono-brom substituted cyclobutene, cyclopentene, cyclohexene, cycloheptenes and the like also fall within the class of compounds which may be subjected to further halo-substitution at moderate and even subatmospheric temperatures, in accordance with the present invention. Furthermore, the partially halogenated secondary oleflns and cyclic oleflns of secondary character of the types described herein may be linked to one or more cycloalkyl and/or aromatic radicals.

The oxygen which is employed in accordance with the present invention acts as an inhibitor of induced addition reactions which occur when the reaction rate is stimulated, for example, under the influence of light or by the use of relatively high halogen concentrations. The induced addition reaction which ordinarily accompanies the halogen substitution reaction when an .olefln of the class described is reacted with a halogen at low temperatures and under reaction stimulating conditions, is the reaction of the halogen with the original halo-substituted compound of the above class to form a more highly halogenated saturated product. Since the oxygen acts as an inhibitor of this induced reaction, in the presence of such oxygen a greater intensity oi stimulation is necessary to maintain a given degree of reaction between the described class of unsaturated, partially halogenated organic compounds and the halogen. In other words, a greater intensity of light, and/or greater concentration of halogen than the maximum may be employed, the oxygen inhibiting the induced addition reaction and thus, in eflect, increasing the rate at which-products of halo-substitution may be formed without the simultaneous formation of excessive quantities of products of induced halogen addition. This inhibiting action of oxygen is substantially proportional to its concentration, so that with higher concentrations of oxygen it is possible to employa greater intensity of stimulation for the unsaturated hydrocarbons of secondary charac-- ter having at least three carbonatoms in the Furthermore, poly-halogenated unreaction under the influence of light. Another molecule and a halogen atom attached to a carbon atom of secondary character, without producing excessive quantities of products of halogen addition. The amount of oxygen therefore depends on the degree of stimulation employed and will vary with practical features of economy. design of plant and the like. It is to be emphasized that the effect is not one of dilution ofireaction by an inert gas, but an active inhibition of the induced addition reaction by the oxygen.

Instead of employing pure oxygen, it is also possible to use air and the like oxygen-containing gases.

the same time, by employing oxygen to inhibit v the induced addition reaction.

The invention is illustrated by the following examples which are presented for the purpose of showing various modes of executing the process, the advantages derived thereby. and the results thus obtainable. It is to be understood,

- however, that the scope of the invention is not The process of the invention is of particular commercial value as applied to the halogenation of 2-chlor-butene-2, which is produced as a byproduct during the manufacture of butadiene- 1,3, from dichlorbutane. Heretofore, many unsuccessful attempts were made to convert this by-product into some useful product. Thus, it was formerly treated with magnesium chloride and calcium chloride on a silica gel support at elevated temperatures in an attempt to convert the 2-chlor-butene-2 into butadiene. However, it was found that only negligible conversion was attainable (Gutner and Tishchenko, Joum. Gen.

Chem., U. S. S. R., vol. 6, pp. 1729-1735). In

fact, the authors definitely state that 2-chlorbutene-2 is highly stable. On the other hand, it has now been discovered that this heretofore undesirable by-product can be subjected to chlorsubstitution to produce a new compound which method of intensifying the reaction is by increasing the rate of fiow of the halogen into the liquid unsaturated monochloride. Also, the reaction rate can be greatly accelerated, for example, by commingling the halogen and the unsaturated organic compound of the defined class in substantially stoichiometrical proportions, and by conveying the mixture through a reaction vessel, especially at relatively low temperatures which will assure a liquid phase reaction, or at least the presence of a liquid film. However, when such reaction stimulating means are employed the products of reaction predominate in 2,2,3-

trichlor-butane which is apparently produced by limited in any sense by the specific data appearing in these examples.

Example I About 3.6 mols of 2-chlorpropene were introduced into a 500 c. 0. glass flask maintained at a temperature of 0 C., and approximately 1.8 mols of chlorine were passed through the liquid chlorpropene at a rate of about 1.5 grams per minute. Two runs were made: in the first, the reaction was illuminated with a 2500 watt lamp,

while in the second run the reaction was effected in the dark and in the presence of oxygen equivalent to 5% of the chlorine introduced. Ananalysis of the reaction products showed that, while in the first case, a yield of 90% of 1,2,2-trichlorpropane was obtained, the presence of the oxygen inhibited chlor-addition so that the reaction product had the following composition:

- Per cent 2,3-dichlorpropene-l 12.5 1,2-dichlorpropene-l 12.4 1,2,2-trichlorpropane 15.1

It is thus'seen that the presence of the relatively small quantities of oxygen greatly inhibited the induced addition reaction caused by the relatively high chlorine concentration. If the second reaction were effected with the oxygen and under the influence of light, it would have been necessary to increase further the oxygen concentration since otherwise the quantity or the trichloride would have increased. Such use of light (and added oxygen) would have further stimulated the reaction so that it would have been possible to increase the rate of chlorine addition without the formation of excessive quantities of saturated chlorine addition products.

Example II A series of batch chlorination runs were made I in a 500 c. c. glass flask containing 2-chlor-buthe aforementioned induced addition reaction.

Owing to the relative difiiculty of converting 2,2,3-

trichlor-butane into any commercially useful tene-2,these runswere conducted both in the dark and. under the influence of light which consisted of a 2500 watt lamp disposed adjacent the reaction vessel. Also, some of the runs were realized in the presence of oxygen which was used in a quantity equivalent to 5% of the chlorine introduced into the reaction vessel. For each run, 3.0 mols of 2-chlor-butene-2 were introduced into the reaction flask, and the chlorine was conveyed therethrough in a quantity of 1.5 mols and at a rate of 1.5 grams per minute. Various temperatures were employed. The following table shows theinfiuence of oxygen on the composition of the resultant product.

Tempera- Unsaturated Saturated ture Oxygen dichloride trichloride 0. Percent Percent Percent 20 No None 73. 8 25. 2 -20 No 5 77. 5 22. 6 40 N 0 None 78. 0 21 (l 40 N0 5 81. 4 1K 6 40 Yes None 37. 4 62. 6 40 Yes 5 70. 7 29. 3

The unsaturated dichloride obtained by the above substitution of chlorine into 2-chlor-bu- I stimulated by light.

tene-2 is a new compound, 2,3-dichlor-butene-1, I

boiling at 1 1l.8 C.,' having'a specific gravity of and a refraction index of Its structure was established both by ozonization I and by allylic rearrangement to 1,2-dichlor- I 'but'ene-2, whichv boils at about IBM-131 C. The

other 2,3-dihalo butene-l compounds, wherein like or different halogen atoms are attached in the 2-"and 3 positionaare also deemed to be novel compounds,

A comparison of the results obtained in the v a vertical glass reaction tube 1.5 cm. in diameter and 48 cm. long. The reaction tube was jacketed and provided with means for cooling the tube by means of .water (to extract at least a part of the heat of reaction). The mol ratio of the chlorine to the unsaturated monochloride was maintained at about 1:1.7. As shown in the following table some ofthe: runs were effected in the dark, while.

others under the influence or light. Also, the runs were realized both in the absence and presence of relatively small percentages of oxygen,

abovetable shows the advantages derived by the use of oxygen, particularly when the reaction is Thus, referring to run No. 5, whereas only 37.4% of the reaction product comprised an unsaturateddichloride when the reaction was-stimulated by light but was conducted in the absence of oxygen, more than 70% of the reaction product wasobtained by chlor-suhstitu- 1 'tion when effected in the presence of only a small percentage of oxygen. I

Example III In'or der to determinethe inhibiting eifect of small quantities of oxygen on'the' inducedaddition caused by high chlorine concentrations, two experiments or'runs were conducted under the same conditions as those employed inthe con-w ducting of runs 3 and 4 of Example II, except for I the fact that'the chlorine was conveyed through the liquid 2-chlor-butene-2 at a ratecf. about'3i4, grams per minute. In other words, the concen- I tration of 'the'chlorine in the unsaturated monoc hloride was more than doubled. Both runs were I The results obtained by.

' eflecting the reaction with and. without oxygen reallzed in the dark.

A comparison of these two runs with runs 3 and 4 of'Example II, show'the advantages derived by using oxygen when the reaction is stimulated as by an increased chlorine concentration. Thus, when the chlorine throughput was only 1.5 grams per minute, and when the reactions were effected in the dark, the presence of the oxygen increased the yield of 2,3-dichlor-butene-1, by only 3.4%. On the other hand, when the chlorine throughput was increased to 3.4 grams per minute (while maintaining other conditions equal), the oxygen increased the percentage of the unsaturated dichloride from 58.7% to 76.4%, or by 17.7%. It is to be noted that an increase in the chlorine concentration lowered the yield of the 2,3-dichlorbutene-l. However, the rate of reaction increased considerably. Furthermore, by increasing the quantity of oxygen introduced, it is possible to increase further the yield of the unsaturated dichloride, thus simultaneously decreasing the quantity of the saturated trichloride (2,2,3- trichlorbutane) which is formed by the'induced addition reaction.

Example IV.

this percentage being calculated on the chlorine introduced. Thefollowing table shows the influence of oxygen on the composition of the product. l

* Reaction cent Rllll' temp Light Oxygen chlorine molal a I reacting reacting 0. Per cent Per cent 70 No None 100, 0 64 N o 2 99. 6 '60 No I 5 99. 2 .93 Yes None 100.0 32 91 No None 95.0 45 75 No 2 77.0 68 Yes 2 99. 2 46 Comparing the results of the first three runs which were conducted in the dark and at about 6040? (2., it is seen that. although the presence of the oxygen decreases slightly the total percentage of chlorine reacting (from to 99.2%), the yield of'the unsaturated dichloride 2,3-dichlor-butene-1 is more than doubled. At the higher temperature of between about 75 and 90 C., the presence of only,2% oxygen also increases the yield of 2,3-dichlor-butene-l, as compared to that obtainable when the reaction is eifected in the dark or under the influence of light, but in the absence of oxygen.

Example V chlor-butene-2 maintained at 40 C. and in the absence of light. The chlorine stream contained about 5% oxygen. An analysis of the efliuent gases and of the reaction product showed that 66% of the chlorine reacted by allylic substitution to form 2,3,4-trichlor-butene-1 in a yield of 58 mol, per cent. The remainder comprised 1,2,3,3-tetrach1orbutane.

It is to be noted at this time that in all of the above cases of liquid phase chlorination via substitution of the defined class of partially halogenated unsaturated organic compounds the substitution is by the attachment of a chlorine atom to the unsaturated carbon atom which is not already attached to a halogen atom. Simultaneously there is an allylic rearrangement or shifting 'of the double bond, so that, as a result, the

chlor-substitution according to the present process is into allylic position. In view of the above, it is therefore now possible to predict exactly the compound which may be obtained by the low temperatureliquid phasehalo-substitution of the described class of partially halogenated unsaturated organic compounds.-

Example VI Chlorine and 2-chlor-butene-2 were separately preheated to a temperature of about 250 C., and intimately commingledin a molal ratio of 1:43. The heated mixture was then conveyed successively at a rate of about 19.4 grams per minute through three tubular reaction chambers. Each reactor had an internal diameter of 4 cm., was 75 cm. long, and was packed with carbon chips passing through a #4 mesh and retained on #6 mesh. An analysis showed that the composition of the reaction product was as follows:

M01 per cent 1,2-dichlor-butene-2 48 9 1,3-dichlor-butene-2 2.3-dichlor-butene-1 13.9 2,2,3-trichlorbutane 7.6

Total 70.4

The above vapor phase, high temperature chlorination was efiected without the use of any oxygen. The products obtained difier materially from those obtainable by the liquid phase treatment. Thus, only a comparatively small percentage of the resulting product comprised, the

2,3-dichlor-butene-1, which is the predominant product when the reaction is efiected in the liquid phase and in the presence of the oxygen. Thus, the mechanism described herein appears to be definitely inapplicable to the high temperature reactions in the vapor phase.

Ezrampie VII About 1.8 mols of chlonTne were conveyed at a rate of 1.5 grams m1 minute through 2.? mols of liquid 2,3-dichlor-butene-1 maintained at a temperature of between about 35 and 50 C. The reaction was efiected in the dark, but in the presence of oxygen in an amount equivalent to about of the chlorine employed. It was found that approximately 95% of the chlorine reacted by addition to form i,2,2,3-tetrachlorbutane (boiling point 178 C.)

to an unsaturated carbon atom of secondary character, such compounds (if of the polyhalide type) containing halogen atoms attached to carbon atoms which, however, are not in vicinal position to the unsaturated carbon atom to which the first mentioned halogen atom is attached.

In what is stated herein, the term primary .carbon atom refers 'to a terminal carbon atom compounds in which a halogen atom is attached which is attached to only one other carbon atom.

The bond between such carbon atoms may be a single bond, or may comprise an olefinic'or acetylenic linkage. The terms secondary carbon atom or carbon atom of secondary character refer to a carbon atom directly attached (whether by single bonds or by multiple bonds) to two carbon atoms, whereas a tertiary carbon atom is one directly attached to three carbon atoms.

Since the reaction is to be effected in the liquid phase, or at least in the presence of a liquid film in the reaction zone, the temperature will vary with the unsaturated compound subjected to the substitutive halogenation reaction. Since the partially halogenated unsaturated organic compound of the described class is soluble in the reaction product (unsaturated, polyhalide), the upper temperature limit is the boiling point of such reaction product. For example, in the case of the chlorination of 2-chlor-butene-2 according to the present process, the reaction should be efiected below about 112 C., which is the boiling point of the 2,3-dich1or-butene-1. However, generally speaking, lower temperatures are preferred. Thus, in the case of the substitutive chlorination of the 2-chlor-butene-2, the. preferred temperature range is between about 0 C. and C. However, as stated, higher or lower temperatures may be employed. I

The reaction may be effected at any suitable pressure, and may be either of the batch, intermittent or continuous type, as this is shown in the examples. Also, although the examples relate to the chlorination of the described class of partially halogenated unsaturated organic compounds having a halogen attached directly to an unsaturated carbon atom of secondary character, the invention is applicable to reactions in which halogens other than chlorine, such as bromine or iodine, are employed. Furthermore, in lieu of employing a halogen per se, it is also possible to use a compound which yields a halogen under operating conditions.

It is to be noted that in all cases of liquid 1. The process which comprises reacting 2-chlor-butene-2 in the liquid phase with chlorine under the influence of light and in the deliberate presence of oxygen, and then recovering 2,3-di chlor-butene-l from the reaction mixture.

2. The process according to claim 1, wherein the reaction is efiected at temperatures below the boiling point or the reaction product.

3. A process of halogenating via substitution which comprises reacting a 2-halo-butene-2 with a halogen of the group consisting of chlorine, bromine and iodine, and efiecting said reaction in the presence of a liquid phase and of actinic radiations, and in the. deliberate presence oi oxygen, thereby practically inhibiting the formation of products of halogen addition.

i. A process for chlorinating, via substitution,

\ a partially chlorinated unsaturated hydrocarbon containing an olefinic linkage between two non= tertiary'carbon atoms at least one of which is of secondary character and has a chlorine atom attached directly thereto, the carbon atoms in vicinal relationship to this chlorinated unsaturated carbon atom being free from chlorine atoms directly attached thereto, to produce a compound wherein the substituted chlorine is on the car reaction inthe deliberate presenceot oxygen, thereby'inhibiting chlorination via addition.

5. A process for chlorlnating, via substitution,

chlorinated unsaturated hydrocarbon taining an olefimc linkage between two noniary carbon atoms at least one oi which is ndary and has a chlorine atom attached directly thereto, the carbon atoms in vicinal relationshipto this chlorinated unsaturated carbon atom being free from chlorine atoms directly attached thereto, to produce a compound wherein in allyl position with respect to the olefinic linkage, which comprises reacting the partially chlorinated unsaturated hydrocarbon in the liquid phase with chlorine in the deiiberate'preeence of oxygen,- thereby inhibiting chlorination via addition 6.'The process which comprises reacting recovering 2,3-dichloro butene-l from the reaction mixture.

the substituted chlorine is on the carbon atom GEORGE W. HEARNE.