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Friedel-Crafts Alkylation
Summary:
The Friedel-Crafts alkylation reaction proceeds similarly to the acylation reaction, but uses an alkyl halide to attach an alkyl group to an aromatic ring. Anhydrous aluminum chloride is used in this classic example and is extremely hygroscopic and reacts rapidly with water to produce hydrogen chloride fumes. Reference: Friedel-Crafts Alkylation of p-xylene, Experimental Organic Chemistry, Gilbert & Martin, 5th edition, 2011, p. 495 - 496. Chemical Name Aldrich Catalog # Amount per 100 students (g or mL)
EH&S
Purchasing cost per 100 students ($) p-xylene 134449 750 mL $47. Aluminum chloride, anhydrous 237051 35 g $7. 1 - bromopropane B78106 425 mL $59. Crushed ice n/a 500 g n/a Sodium sulfate, anhydrous 239313 250 g $17.
Friedel-Crafts Alkylation – A Greener Approach
Summary:
This alternative Friedel-Crafts Alkylation reaction uses a graphite to catalyze the alkylation of p-xylene by 1-bromobutane. This procedure eliminates the use of aluminum chloride and the associated aqueous work-up of the product. Reference: A Greener Alternative to Aluminum Chloride Alkylation of Xylene, Sereda, G.A. And Rajpara, V.B., J. Chem. Ed., 2007, 84(4), 692 Chemical Name Aldrich Catalog # Amount per 100 students (g or mL)
EH&S
Purchasing cost per 100 students ($) p-xylene 134449 250 mL (^) $24. 2 - bromobutane B 22 mL (^) $7. Graphite (<20 micron particles) 282863 25 g $1. Heptane 246654 750 mL $37.
Friedel-Crafts Acylation – A Greener Approach
Summary:
This greener approach to a Friedel-Crafts acylation avoids the use of aluminum chloride by using an activated alumina catalyst and trifluoroacetic anhydride. The solvent-less reaction is the first step in a 2 - step synthesis of p-anisic acid. Reference: Introducing environmentally benign synthesis into the introductory organic lab - a greener Friedel-Crafts acylation, The Chemical Educator. 2001, 6(1), 25– 27 Chemical Name Aldrich Catalog # Amount per 100 students (g or mL)
EH&S
Purchasing cost per 100 students ($) Anisole 123226 16.5 mL (^) $2. Activated acidic aluminum oxide (Brockmann 1) 199966 150 g $14. Trifluoroacetic anydride 106232 62.5 mL
*C
Glacial acetic acid 695092 17.5 mL (^) $1. Diethyl ether 346136 1500 mL
*F
Sodium bicarbonate, sat. solution S 1500 mL $9. Brine solution 746398 1500 mL (^) $34. Sodium sulfate, anhyd. 239313 250 g $17.
Comparison: Friedel-Crafts
Comparison of Friedel-Crafts Alkylation:
- Greener method eliminates the use of aluminum chloride, which is extremely hygroscopic and reacts rapidly with water to produce hydrogen chloride fumes
- Greener method uses a graphite catalyst which can be re-used to reduce waste
EHS Key: Physical hazard
Toxicity/Health hazard PBT
High hazard Moderate hazard Low hazard Very high hazard No data Other greener lab options to explore:
- A Research-Based Undergraduate Organic Laboratory Project: Investigation of a One-Pot, Multicomponent, Environmentally Friendly Prins–Friedel–Crafts-Type Reaction, J. Chem. Educ. 2012, 89, 265- 267
- A Microwave-Assisted Friedel–Crafts Acylation of Toluene with Anhydrides, J. Chem. Educ., 2013, 90 (3), pp 390 – 392
- The Friedel-Crafts reaction: Acetylation of Ferrocene, Doxsee, K. M., Hutchison, J.E., Green Organic Chemistry – Strategies, Tools, and Laboratory Experiments, Print 2004, pp. 225-230. Purchasing costs Waste (per 100 students) “Greener” benefits Greener method $94.71 1 L liquid waste Traditional method $132.20 1.7 L liquid waste 250 g solid waste
Comparison of Friedel-Crafts Acylation:
- Greener method avoids the use of aluminum chloride, which is highly reactive to moisture, producing hydrogen chloride fumes
- Both methods utilize diethyl ether as a solvent in the work-up procedures, which is highly flammable
- Greener method can be used as part of a multi-step synthesis as product can be used to create p-anisic acid in a second reaction
- Greener method avoids the use of concentrated hydrochloric acid Purchasing costs Waste (per 100 students) “Greener” benefits Greener method $265.01 4.6 L liquid waste (3L aqueous waste) 500 g solid waste Traditional method $246.38 3.2 L liquid waste 250 g solid waste
