Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2000-04-17
2001-03-13
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S197000, C570S198000, C570S211000
Reexamination Certificate
active
06201161
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of reducing the benzaldehyde or benzotrihalide content in a mixture with a compound that boils at about the same temperature. In particular, it relates to adding a benzotrihalide or a benzaldehyde to the mixture to react with the benzaldehyde or a benzotrihalide, respectively, in order to form products having a greater difference in boiling point and therefore are more easily separated by distillation.
When 2,4-dichlorotoluene (2,4-DCT) is reacted with chlorine in the presence of ultraviolet light a mixture of 2,4-dichlorobenzylchloride (2,4-DCBC) and 2,4-dichlorobenzalchloride (2,4-DCBAC) can be made. If the reaction mixture is exposed to moisture, however, some of the 2,4-DCBAC is hydrolyzed to 2,4-dichlorobenzaldehyde (2,4-DCBAL). When the product mixture is distilled, the 2,4-DCBC contains 2,4-DCBAL due to a relative volatility of close to one (boiling points) =248 and 250° C., respectively). The presence of 2,4-DCBAL in the 2,4-DCBC is not acceptable for uses such as making stabilizers, but separation of the 2,4-DCBAL by distillation is time-consuming and costly.
When p-chlorotoluene (PCT) is chlorinated, a mixture of p-chlorobenzalchloride (PCBAC) and p-chlorobenzotrichloride (PCBTC) can be made. Separating the PCBAC by distillation is difficult due to the low relative volatility between PCBAC and PCBTC, reduces distillation yield.
SUMMARY OF THE INVENTION
We have found that a benzaldehyde can be separated from a mixture with a desired compound that boils at about the same temperature by reacting the benzaldehyde with a benzotrihalide. That reaction forms a benzalhalide and a benzoylhalide, which have substantially different boiling points than the desired compound, so the desired compound can be more easily separated by distillation.
Similarly, a benzotrihalide can be more easily separated from a compound that boils at about the same temperature by reacting the benzotrihalide with a benzaldehyde to form a benzalchloride and a benzoylchloride, which have significantly different boiling points.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention is applicable to benzotrihalides and benzaldehydes having the respective general formulas:
where each A is independently selected from halogen, CF
3
, R, or OR, each B is independently selected from halogen, CF
3
, or R, R is alkyl from C
1
to C
10
or aryl from C
6
to C
12
, m is 0 to 3, and n is 0 to 2. Preferably, A is Cl or CF
3
, B is Cl, R is alkyl from C
1
to C
6
, m is 0 to 2, and n is 0 or 1. Examples of benzotrihalides that can be used include benzotrichloride (BTC), o-chlorobenzotrichloride (OCBTC), —-chlorobenzotrichloride (MCBTC), p-chlorobenzotrichloride (PCBTC), 2,4-dichlorobenzotrichloride (2,4-DCBTC), and 3,4-dichlorobenzotrichloride (3,4-DCBTC), 2,5-dichlorobenzotrichloride (2,5-DC BTC). The preferred benzotrihalides are 2,4-DCBTC, 3,4-DCBTC, OCBTC, MCBTC, and PCBTC. Examples of benzaldehydes that can be used include benzaldehyde (BAL), o-chlorobenzaldehyde (OCBAL), m-chlorobenzaldehyde (MCBAL), and p-chlorobenzaldehyde (PCBAL). The preferred benzaldehydes are BAL and OCBAL.
The compound to be removed, either the benzaldehyde or the benzotrihalide, constitutes about 0.05 to about 20 mole %, and more typically about 1 to about 5 mole %, of a mixture with a compound that has a boiling point within −10 to +5° C. of the boiling point of the benzotrihalide or benzaldehyde, and preferably within about −5 to about +5° C. of that boiling point. Typically, the other compound in the mixture will be the corresponding benzotrihalide, benzaldehyde, benzylhalide, benzalhalide, or benzoylhalide.
As an example, 2,4-DCBAL can be separated from a mixture of 2,4-DCBC and 2,4-DCBAC by adding 2,4-DCBTC, which reacts with the 2,4-DCBAL to form additional 2,4-dichlorobenzalchloride (2,4-DCBAC) and 2,4-dichlobenzoylchloride (2,4-DCBOC). Since the 2,4-DCBAC and the 2,4-DCBOC are higher boiling than the 2,4-DCBC, the 2,4-DCBC can now be more easily isolated by distillation.
As another example, PCBAC can be more easily separated from a mixture with PCBTC by reacting the PCBTC with PCBAL to form additional PCBAC and p-chlorobenzoylchloride (PCBOC). The PCBOC is higher boiling than the PCBAC.
To remove a benzaldehyde from a mixture, the amount of benzotrichloride added should be about stoichiometric with the amount of benzaldehyde present in the mixture up to about 10 mole % in excess of stoichiometric; preferably, the amount of benzotrichloride added is about 1 to about 5 mole % in excess of stoichiometric. If a benzaldehyde is added to a mixture to remove a benzotrihalide, the amount of benzaldehyde used should be at least stoichiometric with the amount of benzotrichloride in the mixture. To simplify the separation of products, it is preferable to use the corresponding benzaldehyde and benzotrihalide. The benzotrihalide or benzaldehyde can be added before, during, or after a reaction that forms the benzaldehyde or benzotrihalide, respectively.
The reaction between the benzaldehyde and the benzotrihalide occurs at room temperature; higher temperatures due to the accumulation of reaction heat or to external heating will accelerate the reaction. No catalyst is needed, though about 0.01 to about 1 wt % of a Lewis acid catalyst, such as zinc chloride or ferric chloride, can be used to accelerate the reaction if desired. Before distilling, the reaction should be held at an elevated temperature for a period of time to permit the reaction between benzaldehyde and benzotrichloride to occur. The reaction time, reaction temperature, and catalyst level directly influence the reaction rate and, therefore, the level of benzaldehyde or benzotrichloride in the mixture.
The following examples further illustrate this invention:
REFERENCES:
patent: 4105701 (1978-08-01), Larkin
patent: 4922039 (1990-05-01), Yamada et al.
B. F. Filimonov et al., Zh. Obshch. Khim. (1977), 47(7), 1670, titled “Chlorination of Aromatic Aldehydes by Benzotrichloride in the Presence of Iron(III) Chloride”.
B. F. Filimonov et al., Zh. Obshch. Khim. (1979), 49(5), 1098-1105, titled “Oxygen-Chlorine Carbenoid Exchange Between Aldehydes and Compounds Containing a Trichloromethyl Group”.
Khandare Pravin M.
Lagerwall Dean R.
Thielen Daniel R.
Brooks Anne E.
Fuerle Richard D.
Occidental Chemical Corporation
Siegel Alan
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