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Review

Development of Efficient and Selective Processes for the Synthesis of Commercially Important Chlorinated Phenols

by 1,* and 2,*
1
School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK
2
Cornea Research Chair, Department of Optometry, College of Applied Medical Sciences, King Saud University, P.O. Box 10219, Riyadh 11433, Saudi Arabia
*
Authors to whom correspondence should be addressed.
Academic Editor: Wim Dehaen
Received: 1 June 2021 / Revised: 21 June 2021 / Accepted: 29 June 2021 / Published: 8 July 2021
(This article belongs to the Special Issue Feature Papers in Organics)
para-Selective processes for the chlorination of phenols using sulphuryl chloride in the presence of various sulphur-containing catalysts have been successfully developed. Several chlorinated phenols, especially those derived by para-chlorination of phenol, ortho-cresol, meta-cresol, and meta-xylenol, are of significant commercial importance, but chlorination reactions of such phenols are not always as regioselective as would be desirable. We, therefore, undertook the challenge of developing suitable catalysts that might promote greater regioselectivity under conditions that might still be applicable for the commercial manufacture of products on a large scale. In this review, we chart our progress in this endeavour from early studies involving inorganic solids as potential catalysts, through the use of simple dialkyl sulphides, which were effective but unsuitable for commercial application, and through a variety of other types of sulphur compounds, to the eventual identification of particular poly(alkylene sulphide)s as very useful catalysts. When used in conjunction with a Lewis acid such as aluminium or ferric chloride as an activator, and with sulphuryl chloride as the reagent, quantitative yields of chlorophenols can be obtained with very high regioselectivity in the presence of tiny amounts of the polymeric sulphides, usually in solvent-free conditions (unless the phenol starting material is solid at temperatures even above about 50 °C). Notably, poly(alkylene sulphide)s containing longer spacer groups are particularly para-selective in the chlorination of m-cresol and m-xylenol, while, ones with shorter spacers are particularly para-selective in the chlorination of phenol, 2-chlorophenol, and o-cresol. Such chlorination processes result in some of the highest para/ortho ratios reported for the chlorination of phenols. View Full-Text
Keywords: selective chlorination; phenols; sulphuryl chloride; sulphur-containing catalysts; aromatic electrophilic substitution reactions; monochlorination; double chlorination; para/ortho-isomer ratio selective chlorination; phenols; sulphuryl chloride; sulphur-containing catalysts; aromatic electrophilic substitution reactions; monochlorination; double chlorination; para/ortho-isomer ratio
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MDPI and ACS Style

Smith, K.; El-Hiti, G.A. Development of Efficient and Selective Processes for the Synthesis of Commercially Important Chlorinated Phenols. Organics 2021, 2, 142-160. https://0-doi-org.brum.beds.ac.uk/10.3390/org2030012

AMA Style

Smith K, El-Hiti GA. Development of Efficient and Selective Processes for the Synthesis of Commercially Important Chlorinated Phenols. Organics. 2021; 2(3):142-160. https://0-doi-org.brum.beds.ac.uk/10.3390/org2030012

Chicago/Turabian Style

Smith, Keith, and Gamal A. El-Hiti 2021. "Development of Efficient and Selective Processes for the Synthesis of Commercially Important Chlorinated Phenols" Organics 2, no. 3: 142-160. https://0-doi-org.brum.beds.ac.uk/10.3390/org2030012

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