Sandmeyer isatin synthesis - tarry material?

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The discussion centers on the challenges faced in synthesizing substituted isatins using the Sandmeyer methodology, specifically during the condensation reaction involving chloral hydrate, hydroxylamine, and 4-ethylaniline. The main issue is the formation of a tarry byproduct that complicates the cyclization step, resulting in lower yields of impure product. The participant notes immediate formation of insoluble crystals, likely aniline sulfate, upon adding aniline, and suspects this may contribute to the tar formation. They seek advice on preventing the precipitation of aniline sulfate to allow for acetanilide precipitation and inquire about the specifics of the aniline solution used, including its color and whether anhydrous or hydrated sodium sulfate was employed. The reaction is conducted at 60-80°C with magnetic stirring for 2-2.5 hours, monitored by TLC, which indicates the formation of two products and complete conversion of aniline.
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Hey everyone!

I am currently working on a project regarding the synthesis of variously substituted isatins using the Sandmeyer methodology, involving the condensation of chloral hydrate, hydroxylamine and substituted aniline (in this case the 4-ethylaniline) to nitrosoacetanilide with following cyclization under strongly acidic conditions to give the isatin.

640px-Synthesis_of_isatin.png


However, I seem to be stuck on the condensation reaction due to the prevalent formation of a tarry material which I have been unable to wash off, and which seems to cause problems in the cyclization-step, giving lower yields of sticky, impure product. If I follow the synthesis described in the following preparation: http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1p0327, I get an immediate formation of insoluble creme/brownish crystals upon addition of the aniline, which i assume is the aniline sulfate. However, after heating of the reaction mixture, the tar seems to form on/in the crystals. How can I prevent the precipitation of the aniline sulfate, to allow the acetanilide to precipitate, and could the precipitation of the aniline sulfate be the cause of the tarry compound?

The reaction takes place in a roundbottomed flask at 60-80°C (oil bath + internal thermometer) with magnetic stirring for 2-2,5 hours. I use TLC to moniter the reaction (EtOAc/heptane 1:1) which consistently shows the formation of 2 products with the complete conversion of the aniline.
 
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Describe the aniline solution you used and how long did you heat it before it boiled? What color was the aniline you used? Did you use the anhydrous sodium sulfate or the hydrate?
 
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