CA1077526A - Preparation of linear dimers of alpha-alkyl styrenes - Google Patents

Abstract

PREPARATION OF LINEAR DIMERS
OF ALPHA-ALKYL STYRENES

ABSTRACT OF THE DISCLOSURE

Linear dimers are prepared by contacting an alpha-alkyl styrene monomer feedstock with a clay catalyst in the presence of a reaction moderating compound.

Description

~7526 ,;
: PREPARATION OF LINEAR DI~RS
~` O~ A:LPH~-~LXYI STYRENES
FIELD OF THE_INVENTION
`~ This invention relates to a process for preparing ~ linear dimers of alpha-alkyl styrenes. More particularly, this ; invention relates to a process for preparing linear dimers of `, alpha-alkyl styrenes from a refined monomer feedstock. This ~; invention provides reaction moderating compounds which afect ;~ the clay catalyzed dimerization of refined alpha-alkyl styrene in such a way as to increase the amount of linear dimers pro-, duced relative to cyclic dimers.
DESCRIPTION OF THE PRIOR ART
Polymers of alpha-alkyl styrenes are compounds which are useful for a wide variety of purposes. Perhaps the most widely useful polymers of alpha-alkyl styrenes are the dimers.
The dimers of alpha-alkyl styrenes are known to be useful as hydraulic fluids, heat transfer fluids, lubricants and plasti-cizers.
Recently~ however, it has been discovered that the dimers of alpha-alkyl styrenes, particularly those of alpha-methylstyrene, can be used as starting materials from which excellent tractive fluids may be prepared. Tractive fluids are ~ fluids having high coefficients of traction which are useful as -~ fluid mediums in tractive drives or devices. Although the technology of trac*ive fluids is at a relatively early stage of development) a basic discussion of this technology may be found in U.S. Patent 3,411,369. The referenced patent includes a discussion of the function o tractive fluids in tractive devices 9 as well as the concept of coefficient of traction.
; 30 The dimers of alpha-alkyl styrene, partlcul~rly those of alpha-methylstyrene~ may be directly transformed into fluids

- 2~

3 ~75;~6 having high coefficients of traction by hydrogenation. The hydrogenation of these dimers to improve their coefficients of traction may be accomplished using conventional hydrogenation techniques. When substantially completely hydrogenated (e.g., less than about 2% unsaturation), these compo~nds are excellent tractive fluids.
The dimers of alpha alkyl styrenes can take various isomeric forms. For example~ the dimers of alpha-methylstyrene are known to take the following foTms:

(1) CH2 = C - CH2 - C - CH3 2,4-diphenyl-4-methyl-1-' ' pentene [~ a linear dimer) (2) CH - C = CH - C - CH3 294-diphenyl-4-methyl-2-3 ' ' pentene (a linear dimer~

(3) CH3 1,1,3-trimethyl-3-phenyl indane 3 (a cyclic dimer) Cd3 While it is generally known that the cyclic dimer (3) is a solid at room temperatures and the linear dimers (1) and (2) are liquids at room temperatures 9 further distinctions between the linear and cyclic forms have not been of concern to the prior artO

.~

1077~26 ; A substantial distinction exists, however, between the cyclic and linear dimers with respect to the usefulness of the tractive fluids derived from them. Thus, although it has been found that the hydrogenated linear and cyclic dimers have similar coeficients of traction ~i.e., 0.094 for a hydrogenated linear dimer of alpha-methylstyrene and 0.090 for a hydrogenated cyclic dimer of alpha-methylstyrene), it has been Tecently discovered that hydrogenated linear dimers have viscosity ;^ characteristics which are more desirable than those of the hydrogenated cyclic dimers. Thus, for example, the viscosity of a h~drogenated linear dimer of alpha-methylstyrene is about 30,000 cen~istokes at -20F. ~-29C.), while the viscosity of a hydrogenated cyclic dimer of alpha-methylstyrene, at that same temperature, is over 200,000 centistokes. This distinc-tion is a very important one since~ in most contemplated applications for tractive devices, the viscosity of the trac-tive 1uid should be below 50,000 centistokes.
The discovery of the usefulness of the dimers o alpha-alkyl styrenes, as starting materials from which tractive fluids may be prepared, substantially increases the need for an economical process by which to produce them. Especially desirable is a process which is capable of producing predom-inantly linear dimers, with a minimum of cyclic dimers.
The presently known methods of preparing dimers from alpha-alkyl styrene monomers fall into three general categories:
~1) non-catalytic methods, ~) acid catalyzed methods and ~3) clay catalyzed methods.
U.S. Patent 2,595,581 describes a process which is representative of the non-catalytic method of preparing the dimers of alpha-alkyl styrenes. According to this process, ' _~1, _ ~L07752G

dimers of alpha-methyls~yrene are prepared by heating alpha-methylstyrene monomer diluted with at least 10% by weight of inert material to a temperature of about 350C. 7 and under sufficient pressure to maintain the monomer in liquid form.
The product obtained is a mixture of dimer and trimer, with a preponderance of dimer.
- Representative of the acid catalyzed processes are those disclosed in U.S. Patents 2,429,719 and 2,646,450.
U.S. Patent 2,429,719 discloses a process wherein an alpha-alkyl styrene monomer is intimately contacted with sul-furic acid of 30% to 65% concentration at temperatures of from 170F. ~76.7C.) to 200F. (93~3~C~)o The reaction generally takes a few hours ~2 - 8) to complete and uses 0.5 to 5 volumes of acid per volume of monomer. Upon completion of the reaction, the product is separated from the acid, neutralized and/or water washed. While this process is capable of producing a predomi-nantly linear dimer product~ with a minimum concentration of cyclic dimers, it is somewhat complicated by the presence of sulfuric acid. Special acid resistant equipment is required, and the need to effectively free the final product of acid contamination adds to the complexity of the process.
U.S. Patent 2,646,450 discloses a process wherein an alpha-alkyl styrene monomer is lntimately contacted with a catalyst which is from 80 to 98% by weight phosphorus oxyhalide and 2 to 20% by weight of a s~rong mineral acid. Typical phos-phorus oxyhalides used are phosphorus oxychloride and phosphorus oxybromide; typical strong mineral acids used are hydrochloric acid, hydrobromic acid and sulfuric acid. The reaction is generally compIeted in from 0.5 to 6 hours. Upon completion of the reaction, the ca~alyst is removed or neutralized by ~77~,Z6 washing the reaction mixture with water or an aqueous solution o~ an alkali. Because of the acid nature of the catalyst used in this process, it has many of the same complications and equipment needs as the sulfuric acid catalyzed process.
Representative of the clay cataly~ed processes are those disclosed by U.S. Patents 2,433,372; 2,450,027 and 3,161,692.
U~S. Patent 2,433,372 discloses a process whereby alpha-methyl paramethylstyrene monomer is heated to at least 150C. and then brought into contact with from 2 to 10~ by weight of an activated clay catalyst, such as Fullers earth.
A vigorous exotherm results and the temperature must be con-trolled by cooling. The temperature is maintained at between 200C. and 250C. until the refractive index (n20) reaches 1.5600 at which point the reaction has been completed. The hot reaction mixture is then filtered to remove the catalyst, and the residue then allowed to cool and set to a crystalline mass. Since this patent describes the product as "the solid dimer", as distinguished from a liquid dimer, such product is probably comprised mostly, if not completely, of cyclic dimer.
U.S. Patent 2,450,027 discloses a process which is very similar to that disclosed by the aforementioned U.S.
Patent 2,433,372 except that in this process the reaction temperature is kept below 200C., a crude feedstock ~as shown by the Examples) is used~ and the final product is a liquid tl.e., mostly linear dimer).
U.S. Patent 3,161,69~ discloses a process wherein 1,1,3-~rimethyl 3-phenylindane (a cyclic dimer) is produced by contacting alpha-methylstyrene monomer with an acid activated montmorillonite-type clay. For this process, a relatively pure monomer feedstock (i.e., 90 - 99~) is preferred, although .~

.. : ~ . .

~775~6 ` ' :, cruder charge materials may ~e used.
;` The clay catalyzed processes for preparing dimers o alpha-alkyl styrenes (including the dimers of su~stituted alpha-alkyl styrenes) have many favorable characteristics. These processes require no special equipment ~ecause neither high < pressure nor strong acids are used. Product separation is simple in that, upon completion of the reaction, the product and catalyst are separated ~y filtration.
It has been found, however, that when relatively pure 10 feedstocks are used in the prior art clay catalyzed processes, such as that disclosed in the aforementioned U.S. Patent 3,161,692, a product having a high concentration of cyclic dimer results. Those clay catalyzed processes used to prepare pro-ducts which are predominantly linear dimer, such as that dis-closed in U.S. Patent 2,450,027, use crude ~feedstocks as starting materials. Although products which are high in cyclic dimer content may be produced by a clay catalyzed process using either crude or relatively pure monomer feedstocks, the known clay catalyzed processes for preparing products which are pre-20 dominantly linear dimer generally use only crude monomer feed-stocks.
Since crude feedstocks contain lower concentrations of actual monomer than do relatively pure or refined feedstocks, their use results in a lower overall process capacity than that which would be possible if feedstocks having higher concentrations of actual monomer were used. That is to say, a clay catalyæed process capable of preparing products which are predominantly linear dimer using a "pure" or "refined" monomer feedstock would have substantially greater capacity than the prior art processes.
30Therefore, a need exists for a new method of preparing linear dimers of alpha-alkyl styrenes. Such a new method should ~7-... ....... . .. . .....

` ` 43-~305A
~3775~G

have the simplicity of the prior art clay catalyzed process, yet be capable of producing linear dimer products having low concentrations of cyclic dimers from refined monomer -feedstocks.
Surprislngly and unexpectedly, a new process has been discovered for preparing linear dimers of alpha-alkyl styrenes.
This new process retains the simplicity of the prior art pro-cesses, uses refined monomer feedstocks and produces products having low concentrations of cyclic dimers.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a new clay catalyzed process for preparing dimers of alpha-alkyl styrenes. It is another object of this invention to provide a new clay catalyzed process for the preparation of linear dimers of alpha-alkyl styrenes. It is yet another object of this invention to provide a new clay catalyzed process for the preparation of linear alpha-alkyl styrene dimers from refined alpha-alkyl styrene feedstocks.
These and other objects, as will be apparent to those skilled in the art, are met by a process which comprises contacting an alpha-alkyl styrene monomer feedstock with a clay catalyst in the presence of a reaction moderating compound.
The feedstock used in the process of this invention may be crude or refined~ although the advantages of this invention over the prior art are most apparent when a refined or pure feedstock is used.
This invention is based on the surprising discovery that the presence of certain compounds in the reaction mi~ture during a clay catalyzed dimerization of refined alpha-alkyl styrene monomer feedstocks affects the reaction in such a way as to subs~antially increase the ratio o~ linear dimers pro-~', .

77~Z6 ~' ,' .
duced. The compounds which have this effect, hereinafter re-ferred to as "reaction moderating compounds", are generally aldehydes, ketones, alcohols or hydroxy esters. These reaction moderating compounds generally have from I to 10 carbon atoms and are generally effective at concentrations of from 0.1% by weight to 10% by weight, based on the weight o monomer feed-stock, of a reaction moderating compound.
D~SCRIPTION OF THE PREFERR~D ~BODI~NTS
_ ; This invention comprises a process for producing ~;
predominantly linear alpha-alkyl styrene dimer products from refined alpha-alkyl styrene monomer feedstocks by contacting the monomers with a clay catalyst at a temperature of from about 50C. to 150C. in the presence of -Erom 0.1 weight per-cent to 10 weight percent, based on the weight of monomer feed-stock, of a reaction moderating compound. A preferred temperature range for conducting this process is 70Co to 130C., and a more preferred temperature range is 90C. to 110C.
In a preferred embodiment of this invention, the reaction moderating compound is selected from the group con-20 sisting of aldehydes, ketones, hydroxy esters and alcohols. !
Preferred are those reaction moderating compounds having from 1 to 10 carbon atoms; more preferred are those having 2 to 8 carbon atoms, and most preferred are those having 3 to 6 car-bon atoms.
In a particularly preferred embodiment of this inven-tion, the alpha-alkyl styrene is alpha-methylstyrene.
Clay catalysts used in the process of this invention are well known to the art. For example, some of them are dis-cussed in those patents referred to in the earlier discussion of the prior art (U.S-. Patents Z,433,372; 2,450,027 and _9 ,.... . . . .. .. ..

; 43-~305A
~C1775ZG
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3,161,692). Preferred are the montmorillonite, bentonite and attapulgite clays. More preferred are montmorillonite and attapulgite clays. Particularly preferred are activated mont-morillonite clays. Most preferred are sulfuric acid treated montmorillonite clays, such as that which is marketed by Chemetron Corporation under the trade name KSF/0.
This invention constitutes a substantial technical advance over the prior art clay catalyzed dimerization pro-cesses because it enables ~he preparation of predominantly linear dimer products using refined monomer feedstocks, while the prior art processes generally produce products having high concentrations of cyclic dimers -from such ~eedstocks. In order to obtain predominantly linear alpha-alkyl styrene dimer pro-ducts using the prior art clay catalyzed processes, it is generally necessary to use a crude feedstock. Because crude feedstocks contain only about 70-80% actual alpha-alkyl styrene monomer as compared to 95-100% actual alpha-alkyl styrene mono-mer in refined feedstocks, the process of this invention yields about one-third more dimer product than the prior art processes from the same amount of feedstock. The use of a more concen-trated feedstock by the process of this invention results in a higher "pay load" than that of the prior art clay catalyzed dimerization processes.
As used herein, the term "predominantly" means 80%
or more. Thus, a dimer product which is "predominantly linear"
is one in which 80% or more of the total dimers present are linear dimers.
The term "crude" as used herein refers to an unrefined feedstock. Thus, for example, a typical "crude" alpha-methylsty-3~ rene feedstock contains only about 70% by weight alpha methylsty-rene monomer, as shown below.

77~i26 TYPICAL CRUDE ALPHA-METHYLSTYRBNE
Components Concentrations ~ we_ght) _ acetone 0.1%
benzene 0.2%
toluene 0~3%
mesityl oxide 2.5%
cumene 20.0%
butyl benzenes 2.0%
alpha-methylstyrene 70.0%
dimethyl benzyl alcohol 0.1%
acetophenone 1.5%
unknowns 3.3%
As used herein, the term "refined" means (a) a eed-stock which is in a relatively pure state, i.e., not having a significant amount of components other than the major one, (b) a feedstock whlch has been concentrated by partial or com- !
plete removal of non-major components, or (c) either ~a) or ; ~b) which has been intentionally diluted. To illustrate the meaning of the term "refined" as used herein, the following examples are given.
(a) Alpha-methylstyrene, which is essentially pure when produced, such as a stream con-taining 95-100% by weight alpha-methyl-;~ styrene, is within the scope of the term "refined".
(b) Crude alpha-methylstyTene, such as that the composition of which is tabulated above, is converted to "refined" alpha-methylstyrene by removing, to a practical degTee, the components contained therein ~ .

i~77SZ6 other than alpha-methylstyrene.
~c) The "refined" alpha-methylstyrene defined in ~a) or (b) is still "refined" despite having been intentionally dLiluted to a lo~er concentration.
Some crude feedstocks contain one or more o~ the reaction moderating compounds of this invention. The use of such cTude feedstocks in the prior art processes dues not, how-ever, accomplish the outstanding results obtainable by the process of this invention.
Thus, for example, a typical clay catalyzed dimeri-zatîon process yields about 80 pounds ~36.3 kg.) of dimer for each 100 po~mds ~45.4 kg.) o actual monomer fed to it. A
process using a crude feedstock containing 70 weight percent of actual monomers would, therefore, yield only about 56% C8Q%
of 70~) of the total input as dimer product. The process of this invention, however, using a refined feedstock (about 95%
actual monomer) and about 5~ by weight of a reaction moderating compound, would yield about 72~ of the total input (feedstream plus reaction moderating compound) as a final dimer product.
Therefore, for the same input, the process of this invention yields about one-third more product than the prior art processes.
The substantial economic advantages of this will ~e apparent to ; those skilled in the art.
As mentioned earlier, the reaction moderating com-pounds o this invention are generally aldehydes, ketones, hydroxy esters or alcohols. Typical aldehydes which may be used as reaction moderating compounds in the practice of this inven-tion include, but are not limited to, butyraldehyde, acetalde-hyde, formaldehyde, propionaldehyde, paraldehyde, paraformalde-43-4305A ~77526 ~: .

hyde, isobutyraldehyde, valeraldehyde, 2-methylpentaldehyde, 2-ethylbutyraldehyde, acrolein, methacrolein, crotonaldehyde and acrolein dimer (2-formy1-3,4-dihydro-2H-pyran). Preferred are butyraldehyde, propionaldehyde, isobutyraldehyde, and crotonaldehyde; most preferred is butyralclehyde.
Typical ketones which may be used as the reaction moderating compounds of this invention include, but are not limited to, mesityl oxide, cyclohexanone, acetone, pentanone-2, methyl isoamyl ketone, methyl isobutyl ketone, methyl ethyl ketone, methyl n-amyl ketone, ethyl butyl ketone, diisobutyl ketone, isobutyl heptyl ketone, isophorone, 2,4-pentanedone and diacetone alcohol. Preferred are mesityl oxide, cyclo-hexanone, acetone and isophorone; most preferred are mesityl oxide and cyclohexanone.
The hydroxy esters whi~h may be used as the reaction moderating compounds of this invention include, but are not limited to, ethyl glycolate, 2-hydroxyethyl acetate, 2-hydroxy-ethyl methacrylate, 2-hydroxypropyl methacrylatej methyl glycolate, butyl lactate, dimethyl malate, diethyl malate, ethyl 3-hydroxybutyrate, methyl 3-hydroxybutyrate and methyl lactate. Preferred are ethyl glycolate, methyl glycolate, dimethyl malate and methyl lactate; most preferred is methyl glycolate.
Typical alcohols which may be used as the reaction ` moderating compounds of this invention in~lude, but are not limited ~o, butanol, methanol, ethanol, propanol, pentanol, 3-methyl-1-butanol, hexanol, 2-methylpentanol, 4-methyl-2-pentanol, 2-ethylbutanol, 2-ethylhexanol, heptanol, octanol, nonanol, and their isomers. Preferred are butanol 9 ethanol and propanol; most preferred is butanol.
' 43-4305A ~
~775'~6 The reaction moderating compounds of this invention may be used either alone or in any combination.
It will be understood by those skilled in the art that various modifications of the operating conditions and reaction moderating compounds discussed herein may be made to achieve results similar to those described, within the spirit of this invention. All such variations are consldered to be within the scope of this invention.
This invention is further illustrated by the following Examples, it being understood that the Examples are merely illustrative and in no way limit the scope of this invention.
EXAMPLE I
A mixture of 500 g. of alpha-methylstyrene ~99%
purity), 25 g. of mesityl oxide, and 5 g. of clay catalyst hemetron KSF/O) was stirred and heated. At about 70Co, an exothermic reaction commenced and external heating was discon-tinued. The temperature was allowed to rise to 100C. and held there by the application of mild cooling. After about 15 minutes, the rate of heat evolution diminished and mild heat was applied to maintain the temperature at about 90-100C.
Samples of the reaction mixture were analyzed at intervals by gas/liquid chromatography; after three hours, the composition of the mixture was changing only slowly. The catalyst was - filtered off. The reaction mixture was distilled to provide 50 g. of forecut (containing mesityl oxide and some unreacted alpha-methylstyrene), and 417 g. of alpha-methylstyrene dimer boiling at 171-175C. at 10 mm. pressure. Gas/liquid chroma-tographic analysis showed the product dimers to be 98% linear and 2~ cyclic. The distillation residue (46 g.) contained higher AMS oligomers (trimers and tetramers).

EXAMPLE II
31 pounds (14.1 kg.) of alpha-methylstyrene (95+%
weight purity) and 1.25 pounds ~0.57 kg.) o mesityl oxide are charged to a stirred reactor. Then, 0.31 pounds ~0.14 kg.) of clay catalyst is charged. The reaction mixture is heated up. ~ .
At between 70C. and 80C., heating is stopped. The exothermic reaction causes the temperature to continue to rise. External cooling is applied to maintain the reaction temperature at 100C. When the reaction temperature is s~abilized at lOQC., 94 pounds ~42.6 kg.) of alpha-methylstyrene are added over a 45-60 minute period. The reaction temperature is held at about 100C, for rom 2 to 8 hours, at which time the reaction is terminated and the reaction mixture is filtered to remove the catalyst from the reaction mixture. The reaction product is distilled to provide about 10 pounds (4.5 kg.) of forecut, 100 .
pounds ~45.4 kg.) of linear alpha-methylstyrene dimer~ and 16 pounds ~7.3 kg.) of distillatîon residue. The dimer product contains about 95-98 weight percent linear dimer and 2-5 weight percent cyclic dimer.
EXAMPLE III
-A mixture of 200 g. of alpha-methylstyrene C99%
purity), 10 g. of butanol and 0.5 g. cla~ cata~yst (Chemetron KSF/O) was heated and stirred as in Example I. Distillation provided 155 g. of alpha-methylstyrene dimer having a linear to cyclic ratio of 96:4.
EXAMPI,E IV
A mixture of 200 g. of alpha-methylstyrene C99%
; purity~, 2 g. of ~utyraldehyde and 0.5 g. of clay catalyst ~Chemetron KSF/O) was heated and stirred as in Example I.
After 1 hour at 100C., the GLC analysis indicatecl that the ` ` 43-4305A
1~:B77S2~i ~

reaction mixture contained a linear to cyclic dimer ratio of 90:10.,' EXAMPLE V
A mixture of 200 g. of alpha-methylstyrene ~95+%
purity), 5 g. of methyl glycolate and 1 g. of clay catalyst is heated at 90-100C. as described in Example I. Piltration and distillation provide an 80~ yield of alpha-methylstyrene dimer having a linear to cyclic ratio of 95:5.
EXAMPLE VI
(No reaction moderating compound used).
A mixture of 200 g. of alpha-methylstyrene (99%
purity} and 0.2 g. of clay catalyst (Chemetron KSF/O) was heated and stirred. At between 40C. and 50C., an exothermic reaction began; external heating was removed. The reaction temperature was held at about 90C. by the application of an ice and water cooling bath. After an hour, the mixture was filtered. GLC analysis indicated that the mixture contained alpha-methylstyrene dimers having a linear t~ cyclic ratio of 66:34.
Although the concepts of this invention have been described with respect to the dimerization of alpha-alkyl styrenes in general, and alpha-me*hylstyrene in particular, it will be understood that the scope of this invention extends well beyond these most important embodiments~ For example, the concepts of this invention may be applicable to the dimeri-zation or polymerization of various substituted orms o-f alpha-alkyl styrenes and even to styrene itsel~

Thus, another embodiment of this invention is a process for producing a predominantly linear di~er p-roduct by contacting a refined feedstock of monomers or mixtures thereo-f defined by the structure:

~7752~

(C~2)nH
C=~2 :

tCH2)pH~CH2)mH ~ ~:
wherein m, n and p are each independently an integer from 0 to 3, with a clay catalyst in the presence o~ a reaction moderating compound of this invention. In i prefelred embodi-ment, n = 1, and p + m = 3~ In another preferred embocLiment, n = 1, p = 1 and m = 0. In still another preferred embodiment, the compound represented by the structure is alpha-methyl para-methylstyrene. In a most preferred embodiment, the compound , represented by the structure is alpha-methylstyrene.
An additional feature o~ this invention, which is a substantial economic advantage, is that the reaction moderating compound used in the process of this invention may ~ -be recovered and reusedO Thus 9 the net amount of reaction , moderating compound actually used or consumed by the process ' of this invention can be limited to that which is required to make up for losses, as will be understood by those skilled in the art.
The advantages of this invention are further illus-trated by the results tabulated in Table I, which were obtained from laboratory experiments using the process of ehis invention.

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Claims (13)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A process for producing predominantly linear alpha-alkyl styrene dimer products from refined alpha-alkyl styrene monomer feedstocks by contacting the monomers with a clay catalyst at a temperature of from about 50°C. to 150°C.
in the presence of from 0.1 weight percent to 10 weight per-cent, based on the weight of monomer feedstock, of a reaction moderating compound selected from the group consisting of aldehydes, ketones, hydroxy esters and alcohols.

2. A process as described in Claim 1 wherein the clay catalyst is a montmorillonite or attapulgite clay.

3. A process as described in Claim 1 wherein the reaction moderating compound contains from 1 to 10 carbon atoms.

4. A process as described in Claim 3 wherein the reaction moderating compound contains from 3 to 6 carbon atoms.

5. A process as described in Claim 1 wherein the reaction moderating compound is selected from the group con-sisting of butyraldehyde, propionaldehyde, isobutyraldehyde, crotonaldehyde, mesityl oxide, cyclohexanone, acetone, iso-phorone, ethyl glycolate, methyl glycolate, dimethyl malate, methyl lactate, butanol, ethanol and propanol.

6. A process for producing a predominantly linear dimer product by contacting a refined feedstock of monomers or mixtures thereof defined by the structure:

wherein n, m and p are each independently an integer from 0 to 3, with a clay catalyst in the presence of a reaction moderating compound selected from the group consisting of aldehydes, ketones, hydroxy esters and alcohols.

7. A process as described in Claim 6 wherein the reaction moderating compound contains from 1 to 10 carbon atoms.

8. A process as described in Claim 6 wherein the reaction moderating compound contains from 3 to 6 carbon atoms.

9. A process as described in Claim 6 wherein the reaction moderating compound is selected from the group con-sisting of butyraldehyde, propionaldehyde, isobutyraldehyde, crotonaldehyde mesityl oxide, cyclohexanone, acetone, iso-phorone, ethyl glycolate, methyl glycolate, dimethyl malate, methyl lactate, butanol, ethanol and propanol.

10. A process for producing a predominantly linear alpha-methylstyrene dimer product from a refined alpha-methylstyrene monomer feedstock by contacting the monomers with a clay catalyst at a temperature of from about 50°C. to 150°C. in the presence of from 0.1 weight percent to 10 weight percent of a reaction moderating compound selected from the group consisting of aldehydes, ketones, hydroxy esters and alcohols.

11. A process as described in Claim 10 wherein the reaction moderating compound contains from 1 to 10 carbon atoms.

12. A process as described in Claim 10 wherein the reaction moderating compound contains from 3 to 6 carbon atoms.

13. A process as described in Claim 10 wherein the reaction moderating compound is selected from the group consisting of butyraldehyde, propionaldehyde, isobutyraldehyde, crotonaldehyde, mesityl oxide, cyclohexanone, acetone, iso-phorone, ethyl glycolate, methyl glycolate, dimethyl malate, methyl lactate, butanol, ethanol and propanol.