BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to processes for iodinating substituted aromatic compounds over non- acid catalysts.

Discussion of Background

It has long been desired to be able to derivatize aromatic compounds and in particular condensed ring aromatic compounds in commercially attractive quantities since many of these compounds possess properties which would fill long sought needs. In particular, substituted benzene and naphthalene carboxylic acids or esters are particularly desired for use in the manufacture of polyesters which would have excellent properties when fabricated into films, bottles or coatings. However, known techniques for producing these carboxylic acids and esters are very expensive and impractical for commercial exploitation.

Description of the Prior Art

Synthesis of iodobenzene starting from benzene and iodine is usually carried out in the liquid phase in the presence of an oxidative agent, preferably nitric acid. Such techniques have been described in the literature and in particular in Japanese 58/77830. U.S.S.R. Patent 453392 and by Datta and Chatteriee in the Journal of the American Chemical Society. 39. 437. (1917). Other oxidative agents have also been suggested but none of these have

proven to be more efficient or convenient than nitric acid. Typical of the other oxidative agents which have been suggested are iodic acid, sulfur trioxide and hydrogen peroxide as described by Butler in the Journal of Chemical Education. 48. 508. (1971). The use of metal halogenides to catalyze iodination has been suggested by Uemu a. Noe. and Okano in the Bulletin of Chemical Society of Japan. 47. 147, (1974). The concept of direct iodination of benzene in the gas phase over the zeolite 13X has been suggested in Japanese Patent Publication 82/77631 in the absence of any oxidizing agent.

Ishida and Chono in Japanese Kokai 59/219241 have suggested a technique for oxyiodinating benzene over very acidic zeolite catalyst having a silica to alumina (SiO :A1 0 ) ratio of greater than 10. In this technique benzene is reacted with iodine in the presence of oxygen to produce iodinated benzene. According to this disclosure approximately 96% of the benzene which is converted is converted to iodinated form. However, the remaining benzene is oxidized to carbon dioxide and other combustion products result¬ ing in the loss of valuable starting material.

Other Information

Subsequent to the present invention, Paparatto and Saetti disclosed in European Patent Applications 181.790 and 183.579 techniques for oxyiodination of benzene over zeolite catalysts. European Patent Application 181,790 suggests the use of ZSM-5 and

ZSM-11 type zeolites which has been exchanged prior to use with the least one bivalent or trivalent cation. According to this disclosure the utilization of these zeolites in the acid or alkaline form results in a rapid decrease in catalytic activity in relatively few hours.

European Patent Application 183,579 suggests the utilization of X type of Y type of zeolite in non-acid form. According to 183,579 the X or Y zeolites have to be used in the form exchanged with mono-valent. bivalent or trivalent cations and in particular with alkaline or rare earth cations. The techniques of 181,790 and 183.579 prepare the mono- iodobenzene in selectivities in excess of 90% and only distinctly minor amounts of the diiodobenzene compounds.

BRIEF DESCRIPTION OF THE INVENTION Accordingly, one object of the present invention is the technique for catalytically iodinating substituted aromatic compounds.

Another object is a process for the selective iodination of substituted benzenes over a zeolite catalyst.

A further object of the present invention is the technique of the iodination of substituted naphthalenes over a zeolite catalyst.

These and further objects of the present invention which will become apparent from the following disclosure have been attained by a process which is reacting a substituted aromatic compound over a non-acid catalyst with a source of iodine and a source of molecular oxygen.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The aromatic compounds which can be utilized in practice of the present invention are essentially any substituted aromatic compounds. Here a subεtituent is considered to be a terminal group replacing hydrogen on the parent aromatic species. Suitable aromatic compounds include hydrocarbon aromatics.

nitrogen containing aromatics and sulfur containing aromatics. Typical hydrocarbon aromatics include benzene and biphenyl; condensed ring aromatics such as naphthalene and anthracene; sulfur containing aromatics including thiophene and benzothiophene; nitrogen containing aromatics including pyridine and benzopyridine; and oxygen containing aromatics including furan and benzofuran. Other parent aromatics include diaryl sulfoneε, diaryl ethers, diaryl carbonyls, diaryl εul ides and the like.

Preferred parent aromatics are benzenes, biphenyls and naphthalenes.

Substituents on aromatic compounds which are suitable for the process of the present invention include fluoro. chloro. bro o. iodo, hydroxy. and cyano. Aromatic compounds substituted by alkyl groups are generally not preferred for utilization in the present technique. It has been found that with alkyl substituted aromatics the products are iodinated not only on the ring but also on the side chains. Thus, while alkyl substituted aromatics can be utilized in the present technique their use is not preferred.

The catalysts utilized in the present technique are generally characterized by containing non-acid sites, and more preferably basic sites. The most preferred catalyst for use in one present invention are zeolites in the non-acid form. The zeolites which are chosen must have a pore size at least equal to about the apparent size of the molecule of the substituted aromatic ring compound being reacted. Benzene as well as naphthalene have apparent ring sizes of about 6 A and this the lower limit on the pore size of the zeolite catalyst which is useful. If the aromatic compound cannot enter into the pore

on the zeolite catalyst then only very little conversion of the aromatic compounds will occur. Further, if the zeolite is in the acid form, excessive combustion or oxidation of the aromatic compound will occur which is not preferred. Hence, the preferred zeolites are all in the non-acid form and all contain a pore size of about 6 A or larger.

The type of zeolite which is utilized is not critical so long as greater than 10% of the exchangeable cations are alkali, alkaline earth or rare earth metals and the pore size is greater than about 6 A. In general, the reaction rate is a function of silicon to aluminum ratio in the zeolite. since aluminum is part of the active site. It is preferred to use zeolites of with a silicon (as Si) to aluminum (as Al) ratio of 10:1 or less, more particularly 5:1 or less, still more preferred are those zeolites having a silicon to aluminum ratio of 3:1 or less with the most preferred type having a silicon to aluminum ratio of 1.5 or less. Particular types of zeolites which have proven useful are the X and Y types. The Y type zeolite generally has a silicon to aluminum ratio of about 1.5 to 1 to 3:1. The X type zeolite is generally considered to have a silicon to aluminum ratio of about 1:1 to 1.5:1. The X type zeolite exhibits more sensitivity to the counter ion than the Y type does. That is. the selectivity of this X type zeolite to the production of specific mono, di or tri iodinated aromatic compounds can be altered more successfully with the selection of the appropriate counter ions than can the Y type. While not being bound to any particular theory it is believed that the counter ion affects the selectivity by altering the shape of the active

site thereby increasing or decreasing the selectivity of the catalyst for any particular iεomer as compared with the standard sodium form. As a number of cations at the active site decreases their influence in the shape of the pore decreases and thus selectivity decreaseε. Thuε, when one desires to produce a particular isomer high alumina content zeolites are preferred.

Most of the commercially available zeolites are in the sodium form. The counter ion is easily changed in the zeolite by simple ion exchange and is well known to those skilled in the art. This is generally accomplished by contacting in an aqueous medium a salt of desired counter ion and the zeolite. The period of time over which the contact is conducted and a number of times the ion exchange proceεε iε performed iε dependent upon the degree of replacement which iε deεired.

When the aromatic compound iε a condenεed ring aromatic such as a subεtituted naphthalene, it is preferred that the zeolite contains sodium, potasεium, rubidium and/or cesium counter ions and more preferably potasεium, rubidium or ceεium counter ionε. It haε been found that when the zeolite iε ion exchanged with lithium, calcium, strontium, barium or rare earth metals the condensed ring aromatics are oxidized by the oxygen present in the gas stream to a higher degree. With potaεεium, rubidium and ceεium counter ions present the degree of naphthalene oxidation is εignificantly lesε than 1% of the subεtituted naphthalene iodinated. That iε, esεentially no oxidation of naphthalene occurε with theεe counter ions. When the zeolite is essentially in the sodium form, oxidation of the naphthalene -occurs but to a lesser extent than with lithium.

calcium, strontium, barium and rare earth metal counter ions.

Other compounds which have been proven useful as catalysts in the present invention are non-zeolitic and are characterized as containing alkali or alkaline earth salts. Typical catalysts include magnesium oxide on silica, calcium alυminate, magnesium aluminate, potassium chloride on alumina, sodium sulfate on silica and the like. These catalysts may be supported or unsupported or bound together with a binder to form a shaped particle. Typical supports and binders include silica, aluminum, various clays and the like. In general, any material not containing acid sites can be utilized as the catalyst support. These non-zeolite catalysts generally do not exhibit the selectivity of the zeolite catalyst when producing polyiodated products.

The temperature which the reaction is to be conducted is not critical and can be any temperature which when the aromatic compound is fluid. The maximum temperature at which the process can be carried out is that at which combustion of the aromatic compound occurs. Generally, temperatures of from about 100 to 500°C have been found satisfactory, with temperatures of from 200 to 400°C being preferred, more preferably from about 200 to 350°F. The pressure which the process is conducted is not critical and can range from εubatmospheric to superatmospheric. The utilization of elevated preεsureε in the gaε phaεe proceεε may be preferred εo as to minimize equipment size. In general,

2 pressures from atmospheric to 42 k/cm (600 psig) have proven satisfactory although higher or lower pressures can be utilized. The reaction may be

conducted in either the liquid or the vapor phase.

The molecular oxygen can be introduced as pure oxygen, air or oxygen diluted with any other inert material such as carbon dioxide or water vapor. Essentially oxygen from any convenient source may be utilized. The purpose of the oxygen iε to regenerate the active site on the catalyst to its active form once the iodination reaction has occurred. Thus, the amount of oxygen present during the reaction is not critical. However it is preferred that at least 1/2 mole of oxygen be uεed for every mole of iodine. The molar ratio of iodine to aromatic compound which is to be reacted iε largely determined by whether one deεireε to produce a monoiodinated aromatic product or polyiodinated aromatic product. Stoichio- metrically, 1/2 mole of iodine reactε with 1 mole of aromatic compound to produce the monoiodated form. Similarly, on a εtoichiometric basis 1 mole of iodine is required to convert 1 mole of aromatic compound to the diiodinated form. Greater or leεεer quantities of iodine can be utilized as the artisan may desired. In general, it iε desired to run the process to obtain as close to 100% converεion of the iodine as practical so as to simplify the purifica- tion steps in the recovery of any unreacted iodine. Suggested mole ratios of aromatic compound to iodine to oxygen are from 1:0.5:.25 to about 1:2:3.

Essentially any source of iodine may be employed including elemental iodine (I ), hydroiodic acid in gaseous form, or alkyl iodides, preferably lower alkyl iodides. Furthermore, mixtures of these materials may be used as the source of iodine.

It is anticipated by the present procesε would be carried out continuously by the continuous addition of iodine, oxygen and aromatic compound to

the reactor, however, the procesε can be carried out on a batch or semi procesε as desired. Further, aromatic compound of iodine can be reacted over the catalyst to produce the iodinated product, the addition of the aromatic compound ^' and iodine then being terminated and oxygen then added to the reactor to regenerate catalyst to its active form and then the process commenced again. Alternatively, in a continuous process it is possible to utilize two reactants, circulating the catalyst between them. In the first reactor the iodine and aromatic compound would be added and reacted to form the iodinated compound. The catalyst would then be circulated to the second reactor where it would be contacted with oxygen to be regenerated and then recycled to the first reactor to catalyze additional reactions of aromatic compound with iodine.

The space velocity of the procesε is not critical and may be readily selected by the artisan. Gas hourly space velocity is between 10 and 50.000, preferably between 100 and 20.000 liters per hour of reagents per liter of active zeolite have proven satiεfactory.

The catalyεt iε proven to have an extremely long life and degrades only slowly with time. The degradation of the catalyst is believed to be caused by the decomposition of very small quantities of the aromatic compound which deposits small quantities of carbon on the active sites thereby degrading the catalyst activity. When the reaction conditions are selected such that none of the aromatic starting material iε oxidized, the life of the catalyεt is essentially indefinite. However, when the catalyεt becomes deactivated reactivation iε simple. An excellent regeneration technique is pasεing air or

oxygen over the catalyst for several hours at elevated temperatures. Typically the temperature is above 400°C although higher or lower temperatures are proven equally εatiεfactory. The temperature need only be high enough so as to ensure combustion of the carbon deposit on the catalyst. When pure oxygen iε employed lower temperatures can be utilized, while when air is employed temperatures on the order of about 400°C have proven satisfactory. The following exampleε are preεented to illustrate the preεent invention but are not intended in any way to limit the εcope of the invention which iε defined by the appended claimε.

In the following exampleε. 50 cc of the εtated catalyst was placed in a quartz reactor tube with an internal thermowell. The tube was heated with an electric furnace while the reactantε were added dropwiεe over the catalyεt bed at a rate of 1 ml/ in. Air waε fed cocurrently at 300 ml/min. Productε were collected by condenεing againεt cold water and identified by gaε chromotography-maεε spectrometry and quantified by gaε chromotography (reported aε mole %). All feedε were 0.0341 moleε of iodine per mole of aromatic. A high reaction temperature relative to the furnace temperature indicateε conεiderable combuεtion of the aromatic specieε has occurred, aε doeε a high % CO in the reaction offgas.

EXAMPLE 1

Catalyst: NaX

Furnace temp: 300 deg C

Reaction temp: 302 deg C

Aromatic cpd: benzene The reaction product contained 93.1 benzene.

6.8% iodobenzene, and 0.1% diiodobenzene. The offgas ccoonnttaained <0.2% CO and iodine conversion was

100%.

EXAMPLE 2

Catalyst: NaX Furnace temp: 300 deg C Reaction temp: 302 deg C Aromatic cpd: chlorobenzene The reaction product contained 93.2% chloro¬ benzene. 6.6% chloroiodobenzene. and 0.2% diiodo- chlorobenzenes. The offgas contained <0.2% CO and iodine conversion was 100%.

EXAMPLE 3

Catalyst: NaX Furnace temp: 300 deg C Reaction temp: 450 deg C Aromatic cpd: toluene The reaction product contained greater than 15 separate species. The reaction product was dark and the catalyst deactivated after two hours. The offgas contained 15% CO .

EXAMPLE 4

Catalyst: NaX Furnace temp: 200 deg C Reaction temp: 220 deg C Aromatic cpd: phenol The reaction product contained 92.7% phenol.

1.5% p-iodophenol and 5.8% o-iodophenol. The iodine conversion was 100% and the offgas contained leεε than 0.1% CO„.

EXAMPLE 5

Catalyεt: NaX

Furnace temp: 300 deg C

Reaction temp: 308 deg C

Aromatic cpd: benzonitrile

The reaction product contained 98.5% benzonitrile. 0.7% p-iodobenzonitrile, 0.4% m-iodobenzonitrile, and 0.2% o-iodobenzonitrile, Iodine converεion was 21%.

EXAMPLE 6

Catalyst: 10% KC1-A1203

Furnace temp: 300 deg C

Reaction temp: 302 deg C Aromatic cpd: 1-chloronaphthalene

The reaction product contained 95.1% l-chloro- naphthalene and 4.9% chloroiodonaphthalenes. The iodine converεion waε 70%.

COMPARATIVE EXAMPLE 7

Catalyεt: NaX Furnace temp: 300 deg C Reaction temp: 302 deg C Aromatic cpd: nitrobenzene The reaction product contained over 99% nitrobenzene, with traces of iodobenzene and benzene. Nitrobenzene appears to be unreactive under these conditions.

EXAMPLE 8

Catalyst: NaX

Furnace temp: 300 deg C

Reaction temp: 302 deg C

Aromatic cpd: benzophenone

The reaction product contained 95.2% benzo- phenone and 4.7% iodobenzophenones. The iodine conversion was 67% and the offgas contained less than 0.1% CO .

EXAMPLE 9

Catalyst: NaX

Furnace temp: 300 deg C

Reaction temp: 306 deg C Aromatic cpd: pyridine

The reaction product contained 97.2% pyridine and 2.8% iodopyridines. The iodine conversion was 40%.

While the invention has been described in detail with particular reference to preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention.