Process for preparing iodinated substituted aromatic compounds

A process for iodinating an aromatic compound in which a source of iodine is reacted with the aromatic compound in the presence of oxygen over a non-acid catalyst wherein the aromatic compound has a fluoro, chloro, bromo, iodo, hydroxy or cyano group.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to processes for iodinating substituted 
aromatic compounds over non-acid catalysts. 
2. 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 No. 58/77830, U.S.S.R. Pat. No. 
453392 and by Datta and Chatterjee 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 
Uemura, 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 No. 59/219241 have suggested a technique 
for oxyiodinating benzene over very acidic zeolite catalyst having a 
silica to alumina (SiO.sub.2 :Al.sub.2 O.sub.3) 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 resulting in the loss of valuable starting material. 
OTHER INFORMATION 
Subsequent to the present invention, Paparatto and Saetti disclosed in 
European Patent Application Nos. 181,790 and 183,579 techniques for 
oxyiodination of benzene over zeolite catalysts. European Patent 
Application No. 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 No. 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 monoiodobenzene 
in selectivities in excess of 90% and only distinctly minor amounts of the 
diiodobenzene compounds. 
RELATED APPLICATIONS 
Copending applications Ser. Nos. 912,806, filed Sept. 29, 1986; 029,959 
filed Mar. 25, 1987; 029,898 filed Mar. 25, 1987 disclose techniques for 
iodinating aromatic compounds over non-acid catalysts. Copending 
applications Ser. Nos. 029,899 filed Mar. 25, 1987; 029,956 filed Mar. 25, 
1987; and 029,949 filed Mar. 25, 1987 disclose 
traniodination/isomerization reactions which may be used in conjunction 
with an oxyiodination reaction. 
The disclosures of these applications are incorporated herein by reference. 
These applications do not address the iodination of substituted aromatics, 
however. A need exists for a technique by which substituted aromatics may 
be iodinated. 
BRIEF DESCRIPTION OF THE INVENTION 
Accordingly, one object of the present invention comprises the technique 
for catalytically iodinating substituted aromatic compounds. 
Another object comprises a process for the selective iodination of 
substituted benzenes over a zeolite catalyst. 
A further object of the present invention comprises 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 comprises 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 
substituent 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 
sulfones, diaryl ethers, diaryl carbonyls, diaryl sulfides 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, bromo, 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 catalyst which may be employed in the present technique are described 
in copending applications Ser. Nos. 029897, filed Sept. 29, 1986, 029899, 
filed 3-25-87. The disclosure of these applications incorporated herein by 
reference for a more complex description of the catalyst in reaction 
conditions which are to be employed. 
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 .ANG. 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 .ANG. 
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 .ANG.. 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 zeollite 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 isomer 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 decreases. Thus, 
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 process is performed is dependent upon 
the degree of replacement which is desired. 
When the aromatic compound is a condensed ring aromatic such as a 
substituted naphthalene, it is preferred that the zeolite contains sodium, 
potassium, rubidium and/or cesium counter ions and more preferably 
potassium, rubidium or cesium counter ions. It has been found that when 
the zeolite is 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 potassium, rubidium and 
cesium counter ions present the degree of naphthalene oxidation is 
significantly less than 1% of the substituted naphthalene iodinated. That 
is, essentially no oxidation of naphthalene occurs with these 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 aluminate, 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 at 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.degree. to 500.degree. C. have been found satisfactory, 
with temperatures of from 200.degree. to 400.degree. C. being preferred, 
more preferably from about 200.degree. to 350.degree. C. 
The pressure which the process is conducted is not critical and can range 
from subatmospheric to superatmospheric. The utilization of elevated 
pressures in the gas phase process may be preferred so as to minimize 
equipment size. In general, pressures from atmospheric to 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 is 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 used for every mole of 
iodine. The molar ratio of iodine to aromatic compound which is to be 
reacted is largely determined by whether one desires to produce a 
monoiodinated aromatic product or polyiodinated aromatic product. 
Stoichiometrically, 1/2 mole of iodine reacts with 1 mole of aromatic 
compound to produce the monoiodinated form. Similarly, on a stoichiometric 
basis 1 mole of iodine is required to convert 1 mole of aromatic compound 
to the diiodinated form. Greater or lesser quantities of iodine can be 
utilized as the artisan may desire. In general, it is desired to run the 
process to obtain as close to 100% conversion of the iodine as practical 
so as to simplify the purification steps in the recovery of any unreacted 
iodine. Suggested mole ratios of aromatic compound to iodine to oxygen are 
from 1:0.5:0.25 to about 1:2:3. 
Essentially any source of iodine may be employed including elemental iodine 
(I.sub.2), 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 that the present process would be carried out 
continuously by the continuous addition of iodine, oxygen and aromatic 
compound to the reactor, however, the process can be carried out on a 
batch or semi batch process 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 
betwen 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 process 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 satisfactory. 
The catalyst is 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 is oxidized, the life of 
the catalyst is essentially indefinite. However, when the catalyst becomes 
deactivated reactivation is simple. An excellent regeneration technique 
comprises passing air or oxygen over the catalyst for several hours at 
elevated temperatures. Typically the temperature is above 400.degree. C. 
although higher or lower temperatures are proven equally satisfactory. The 
temperature need only be high enough so as to ensure combustion of the 
carbon deposit on the catalyst. When pure oxygen is employed lower 
temperatures can be utilized, while when air is employed temperatures on 
the order of about 400.degree. C. have proven satisfactory. 
The following examples are presented to illustrate the present invention 
but are not intended in any way to limit the scope of the invention which 
is defined by the appended claims. 
In the following examples, 50 cc of the stated catalyst was placed in a 
quartz reactor tube with an internal thermowell. The tube was heated with 
an electric furnace while the reactants were added dropwise over the 
catalyst bed at a rate of 1 ml/min. Air was fed cocurrently at 300 ml/min. 
Products were collected by condensing against cold water and identified by 
gas chromatography-mass spectrometry and quantified by gas chromotography 
(reported as mole %). All feeds were 0.0341 moles of iodine per mole of 
aromatic. A high reaction temperature relative to the furnace temperature 
indicates considerable combustion of the aromatic species has occurred, as 
does a high % CO.sub.2 in the reaction offgas.