PTC Tip of the Month q-value and C# for Catalyst Structure-Activity

The "q-value" and "C#" are two empirical parameters which are used to characterize the structure of quaternary ammonium salts for structure-activity relationships. C# is simply the total number of carbons on the 4 alkyl chains. Thus, the C# for methyl tributyl ammonium is 1 + 4 + 4 + 4 = 13. As the C# increases, the organophilicity increases and usually results in a higher concentration of the quat-anion pair in the organic phase. When the rate determining step is the organic phase reaction ("I-Reaction"), C#'s in the range of 16 to 32 often provide desirable reactivity. The "q-value" parameter is often useful when the rate determining step is mass transfer ("T-reaction"), especially when using hydrophilic anions such as hydroxide (about half of PTC applications fall in this category). The q-value is calculated by adding the reciprocals of the number of carbons on each of the four chains of the quat. Thus, the q-value for methyl tributyl ammonium is 1/1 + 1/4 + 1/4 + 1/4 = 1.75. For T-reactions, quats with q-values in the range of 1 to 2 often promote desirable reactivity, with q-values of 1.5 to 1.75 often being the best. For more information, please contact Marc Halpern at tel +1 856-222-1146 or by E-mail.


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The course "Practical Phase-Transfer Catalysis" will be conducted in Chicago and Newark later in 2004 and 2005. Can't come to the course? Soon you will be able to purchase just the manual or the manual with a transcript of the course. "Practical Phase-Transfer Catalysis" can also be conducted at your company anytime (North America, Europe or Japan) as a private in-house course. More than 530 chemists, engineers and managers at nearly 100 companies have participated in this highly rated course from 1996 to 2004. Click here for details and agenda or contact us by E-mail or telephone (+1 856-222-1146) or fax (+1 856-222-1124).

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PTC Reaction of the Month Secondary Alcohol to Secondary Alkyl Chloride

It can be challenging to convert secondary alcohols to secondary alkyl chlorides in high purity and avoiding the use of thionyl chloride with stoichiometric pyridine. This patent uses tetrabutyl ammonium chloride to significantly reduce the reaction time (36 h to 8 h) in the selective reaction of secondary alcohols with cyanuric chloride, e.g., to form 6-undecyl chloride. At 99% conversion of 6-undecyl alcohol, the key byproducts are undecene (20%) and diundecyl ether (4%). Extremely low isomerization is observed.  Neumann, M.; Osterholt, C. (Degussa) US Patent 6,756,513 29-June-2004

PT Catalyst of the Month Tetrapropyl Ammonium Bromide

Usually works well in T-reactions due to q-value of 1.33. Easier to extract into water than TBAB (less residual catalyst in product while generating less aqueous waste). Usually much more stable than quats with ethyl groups in the presence of NaOH. Also used as a template for zeolites.
Usually less reactive than TBAB in I-Reactions due to lower C#.
Catalyst Structure
q-value = 1.33; C# = 12

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Before performing any PTC reactions read this important message
Organic chemical reactions are inherently dangerous. Moreover, phase-transfer catalysis may provide rate and other enhancements which can intensify associated hazards. Under no circumstances should anyone perform any procedure on any scale based in whole or in part on any of the contents of this information provided here before thoroughly establishing safe operating procedures and performing a full and competent hazardous operations analysis with the participation of qualified technical personal trained in chemical, engineering, safety, industrial hygiene and environmental disciplines and sciences.

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PTC Tip of the Month #22 - July 2004
Copyright 2004 PTC Communications, Inc.

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