Tie-Dye Grignard Synthesis
4-Bromo-N,N-dimethylaniline underwent a Grignard reaction with diethyl carbonate to produce a type of the tie-dye chemical triarylmethane. This specific triarylmethane produces a vivid crystal violet color when dyed. The experiment was first heated under reflux to produce the necessary Grignard reagent as a grey liquid. It was then reacted with diethyl carbonate and hydrochloric acid to produce crystal violet. The resulting chemical was very absorbent to polypropylene and bleached cotton fabrics. Introduction:
In this experiment a Grignard reaction is performed with a Grignard reagent acting as the nucleophile1. Grignard reactions are very useful for the substitution of compounds containing magnesium onto other compounds. The magnesium on a Grignard reagent withdraws electron density from the attached carbon giving it a partial negative charge1 (Figure 2). This allows the Grignard reagent to be used as a nucleophile in a substitution reaction1. The dye methyl violet is produced from a Grignard reaction in this experiment.
In order to prepare the Grignard reagent used in this experiment it must be heated under reflux. Reflux heating is performed by heating the reaction to its boiling point and allowing it to vaporize and condense inside of a reflux condenser2. No reactant or solvent is lost in this method2. A reflux ring will generally appear within the reflux condenser showing a working reflux reaction. Reflux heating is useful as it allows volatile reactions to be performed quickly. Discussion:
In this experiment a Grignard reagent (Figure 3) was prepared out of 4-Bromo-N,N-dimethylaniline and reacted under reflux with magnesium, tetrahydrofuran, and an iodine crystal with magnetic stirring.
The reaction proceeded by turning a dark yellow or tan color, followed by bright green, tan again, then a dark brown-gray. The product was supposed to turn a dark gray but ended up being browner likely due to the addition of too many iodine crystals by accident. The reagent was then reacted with a solution of diethyl carbonate and tetrahydrofuran to produce the dye methyl violet (Figure 1). This caused the solution to turn a dark blue until hydrochloric acid was added to turn the solution to violet. When hydrochloric acid was added a solid precipitate formed. The resulting dye was absorbent to the fabrics bleached cotton and polypropylene. If the experiment were to be performed again more caution would be taken to make sure the smallest amount of iodine was added. Conclusions:
The prepared Grignard reagent was reacted with diethyl carbonate to produce the dye methyl violet. The reaction was successful even though the Grignard solution did not originally turn the desired dark grey. The resulting crystal violet dye was of expected color and had a strong absorbency to the fabrics bleached cotton and polypropylene as indicated by the test fabric swatch. Experimental:
All reagents used were obtained from the reagent hood and all glassware used was obtained from the provided glassware kits. Reagents were not further modified unless written. Reaction was heated under reflux with magnetic stirring and then cooled in water bath. Product was dyed with a fabric swatch. Methyl Violet. 4-Bromo-N,N-dimethylaniline (2.002 g) was reacted with magnesium (0.249 g), tetrahydrofuran (19.95 ml), and Iodine (1 crystal) under reflux at 70-75 °C for 30 minutes with magnetic stirring. Reaction turned gray and was cooled to room temperature with a water bath. A mixture of diethyl carbonate (0.39 g) and tetrahydrofuran (3.05 ml) was prepared and added drop wise to Grignard reagent. Reaction was refluxed for 5 minutes and cooled to room temperature. Hydrochloric acid (7-9 ml est.) was added and solution turned crystal violet with a solid precipitate formed in flask. Resulting dye was dyed with a fabric swatch.
Gilbert, John C., Stephen F....
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