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PTC Tip of the Month
Choosing Leaving Group for PTC Reactions

Quaternary ammonium phase-transfer catalysts sometimes experience "poisoning" by highly polarizable or lipophilic leaving groups, most notably iodide and tosylate. In one application, an alcohol was converted to a sulfonate ester for displacement. Using the mesylate gave 95% yield whereas using the tosylate gave 5% yield! These are both good leaving groups, however the quat pairs more strongly with tosylate than mesylate which in turn hinders the ability of the quat to transfer and react the desired nucleophilic anion. Guideline: Consider bromide instead of iodide and mesylate instead of iodide.

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PTC Reaction of the Month
Selective Etherification

It is possible to achieve high yield with extremely high selectivity to prepare an ether-ester in the presence of a pre-existing ester group with extremely low levels of hydrolysis. PTC Organics was able to achieve greater than 99.9% selectivity at 99.99% conversion for an ether-ester shown below which is used as an intermediate for 2-ethoxybenzoic acid which is the starting material for Viagra. Two surprising aspects of this process are related to the high selectivity without hydrolyzing the ester: [1] a low excess of ethylating agent was used and [2] the base was NaOH. PTC Organics is seeking to license this technology to an interested manufacturer.

Phase-Transfer Catalyst of the Month
Tetraethyl Ammonium Bromide

Advantages
Provides high reactivity for most PTC "T-reactions" which work well without extended heat history.  Easy to separate from product by extraction into water. Inexpensive. Low molecular weight.
Disadvantages
Has the lowest stability in the presence of base among common N-quats, due to the high susceptibility of the ethyl group to Hofmann decomposition. TEA Br is a poor catalyst for most PTC "I-Reactions."
Reactivity Parameters (Contact PTC Organics for explanation)
Organophilicity is low with C# = 12. Accessibility is high with q-value = 2.0

Availability, Samples and Quotes from Competitors
Request samples and quotes from: Delta Finochem, Dishman Pharmaceuticals & Chemicals, GFS Chemical, Lion Akzo, Nehachem, SACHEM, Tatva Chintan (click on link)

Other Phase-Transfer Catalysts:
PTC Supplier Directory: choose from a dozen suppliers & 80 PT catalysts and ask for free samples & quotes.

Inexpensive patent attorney (United States) familiar with Phase-Transfer Catalysis, organic chemistry and biochemistry. Contact Mannie Morgenstern by E-mail or at telephone 818-788-5531 (California). 

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New PTC Service
PTC Option Go/No-Go Consultation

Purpose
Provide a quick and cost-effective key decision aid during initial project planning, whether to pursue evaluation of phase-transfer catalysis as an option to achieve success or breakthrough performance for an organic reaction/process, consisting of uniquely qualified expert opinion and supported by 28 years of PTC experience and documented evidence.

Benefit & When To Use
Can be crucial to achieve highly effective R&D for organic chemical reactions/processes during process improvement, route selection, overcome challenging selectivity requirements, new process development, process retrofit for breakthrough performance and process optimization

Deliverables
PTC Organics will deliver a written confidential "PTC Option Opinion" for a specific organic reaction which will include: [1] a discussion of the factors anticipated to most likely influence the probability of success of the PTC option for your specific application, [2] an estimated probability of success for the specific application and [3] recommendation for go/no-go decision (does not include experimental program design).

Initiating the Project
To initiate project or obtain attractive pricing for 2005 budget planning, contact Marc Halpern at tel +1 856-222-1146, fax: +1 856-222-1124 or E-mail.

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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.

Policy
The list of PTC Tip of the Month subscribers will not be sold, rented or transferred and will be used only by PTC Communications, Inc. and PTC Organics, Inc. to provide information related to Phase-Transfer Catalysis. PTC Communications, Inc. reserves the right to distribute the PTC Tip of the Month to selected industrial chemists, engineers and managers.

PTC Tip of the Month #26 - November 2004
Copyright 2004 PTC Communications, Inc.

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