Advice on Setup to React Natural Resin Esters

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Discussion Overview

The discussion centers on the setup and methodology for esterifying natural resins such as copal, amber, and dammar. Participants explore the technical aspects of the reaction process, including temperature management, glassware suitability, and the use of various materials in the setup. The conversation includes concerns about high-temperature reactions and the implications for equipment and product quality.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant outlines a detailed procedure for esterifying natural resins, expressing concerns about the high temperatures affecting glassware and joints, particularly regarding the use of PTFE sealing rings and stopcocks.
  • Another participant suggests that the PTFE in the addition funnel may not reach the same temperatures as the reaction pot and recommends using Apiezon H grease instead of silicone grease to avoid contamination in the varnish.
  • There is a recommendation to use sand for heating rather than zinc granules, with a note on the temperature limits of heavy wall borosilicate glass being over 400°C.
  • A participant inquires about suitable stirrer assemblies, expressing concern over the temperature compatibility of Teflon bearings and considering glass or stainless steel alternatives.
  • One participant raises a question about the best method for refluxing glycerin while allowing water to escape, suggesting the use of a Dean-Stark setup instead of a simple reflux condenser.
  • Another participant provides information on the boiling points of glycerol and water at a specific pressure, questioning the likelihood of codistillation and suggesting that other volatiles may be present in the resin.

Areas of Agreement / Disagreement

Participants express varying opinions on the suitability of materials and methods for the reaction setup. While some suggestions are agreed upon, such as the use of Apiezon H grease, there remains uncertainty regarding the best practices for managing high temperatures and the specifics of refluxing glycerin.

Contextual Notes

Participants note the importance of considering the upper temperature limits of materials used in the setup, as well as the potential for codistillation of volatiles during the reaction process. There are unresolved questions regarding the best stirrer assembly and the optimal refluxing method.

GeorgeOh
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I am trying to create esters from natural resins (Copal, amber, dammar, etc.). This is based on chemistry from the first half of the 20th century. The esterified resins were used in making varnishes, before the advent of acrylic and other synthetic resins.

To esterify the natural resins, I must first fuse the resin (called ‘running’) by melting at temperatures of 300° C. for one to two hours. I will run the resins in a round bottom flask with a reflux condenser. Then I will lower the temperature to 260° to 280° C. and add the esterifying agents (glycerin, phthalic anhydride, pentaerythritol, etc.) and react this mixture for another two to four hours. The esterifying agents will be added dropwise through an addition funnel. Then linseed oil or other drying oil will be added to the mixture at 200° C. to complete the varnish.

I do not have a lot of experience with setting reactions of this type, just distillations at lower temperatures. I am concerned about the high temperatures of this reaction and how it may affect the glassware and the joints, especially since I was planning to use Glindemann PTFE sealing rings in the joints and a PTFE stopcock on the addition funnel. I know the upper temperature range of PFTE is supposed to be about 220° to 240° C. Does anyone see a problem with this setup? Would I be better off with silicone grease?

I planned to heat the flask in either a sand bath or replace the sand with zinc granules (30 mesh) to get better heat transfer. Does anyone have experience with metal powders, especially zinc in sand baths?

One more note: The glassware I have is made of heavy wall borosilicate glass. I get conflicting ideas about the upper temperature for this type of glassware.
 
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No problem with the setup. The PTFE in the addition funnel won't get as hot as the pot (hopefully), but if it does you can switch it out for a ground glass one with Apiezon H grease. I wouldn't use silicone for any application for a varnish or coating since the silicones can depolymerize and volatilize into your product. No use having a release agent as a contaminant in your varnish!

No need to use zinc granules, sand will work fine. The upper temperature limit for the borosilicate glass is over 400C if you get the extreme service glass.
Don't cool it too fast.

You will probably need to wrap the flask and lower neck of the condenser with fiberglass roving and... DON'T USE WATER IN THE CONDENSER!

Use low pressure air from house air. Attach the air to the top nipple and leave the lower nipple unconnected. You don't want a rubber hose down there where its hot. Good luck.
 
chemisttree said:
The PTFE in the addition funnel won't get as hot as the pot (hopefully), but if it does you can switch it out for a ground glass one with Apiezon H grease.
Thank you for the valuable suggestions -- they make a lot of sense. Apiezon H Grease is expensive, but I imagine it should last awhile.
 
Stirrer Assembly

Do you have recommendations for the type of stirrer assembly I should use with this setup? I have a Teflon bearing and glass rod, but I am concerned that the temperature of the flask will be too high for the Teflon bearing. I am thinking that a glass bearing will be more suitable. What type of glass bearing and rod should I use? Some of the glass rods are unground and ground and the bearings have a mercury cup or not at the top. Or is a stainless steel rod better?
 
Refluxing Glycerin

I appreciate the assistance from individuals in this forum, but I have one more question regarding this setup: In the initial runnning of the resin, I must allow volatiles to escape from the reaction, but when adding the glycern or other polyhydric alchohol, I must allow water from the reaction to escape, but reflux glycerin so that it can continue in the reaction. Is this best done with a Dean-Stark setup instead of simply a reflux condenser?
 
This is something you should determine for yourself. The BP for glycerol at 200 torr is 240 C. That of water is about 65 C at that pressure. Is it likely to codistill?
 
chemisttree said:
This is something you should determine for yourself. The BP for glycerol at 200 torr is 240 C. That of water is about 65 C at that pressure. Is it likely to codistill?
It is unlikely. There may be other volatiles in the resin that will be distilled off, but these should be eliminated prior to adding glycerin or other polyhydric alcohol.
 

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