Advice on Setup to React Natural Resin Esters

[GeorgeOh]

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.

 

[chemisttree]

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.

 

[GeorgeOh]

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.

 

[GeorgeOh]

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?

 

[GeorgeOh]

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?

 

[chemisttree]

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?

 

[GeorgeOh]

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.