Benzaldehyde is a useful chemical in many pharmaceutical syntheses. A great it example is it's use to prepare mandelic acid, or cinnamic acid. It is also used as an artificial flavor, specifically almonds, or bitter almonds. It has a very sweet smell, not unlike nitroaromatics. Pure benzaldehyde is a clear, colorless liquid. It can be prepared by the sommelet reaction of benzyl chloride, or by the hydrolysis of benzal chloride.
Into a 1000ml flask, add 45g of hexamine. Prepare either a 60% ethanol solution by mixing 80ml of ethanol in 55ml of distilled water, or a 50% acetic acid solution by mixing 80ml glacial acetic acid with 80ml of distilled water. Swirl the flask at least enough to dissolve all visible solids - it doesn't have to become a completely clear solution, you just don't want a cake of hexamine at the bottom. Add 35ml of benzyl chloride to the flask and fit the reflux column to the flask. If you used ethanol, you can use a water bath, otherwise, use an oil bath to heat it to reflux and hold it there for about two hours. Prepare a ~10% solution of hydrochloric acid by mixing 20ml of 31.45% with 40ml of distilled water, or 30ml of 20% with 30ml of distilled water. After the materials in the flask have refluxed for two hours, add the above solution of hydrochloric acid to it and continue refluxing for at least 15-20min. After this, remove the flask from the bath and let it cool to room temp. You should see two layers, the bottom layer is usually a light orange and the top layer can be yellow to orange. The top layer is your benzaldehyde.
Set the flask up for simple distillation and begin heating it on an oil bath. You will now be steam distilling the benzaldehyde from the reaction mixture/by products. After many tests, I have found this to be the most efficient (and easiest method) to obtain the benzaldehyde. If you used ethanol, collect the first fraction all the way up to ~98C. Now, collect everything else distilling over (whether you used ethanol or acetic acid) until the distillate is running out is mostly clear and benzaldehyde free. You may need to add more water to the distillation flask to aid in the steam distillation.
If you used ethanol, take the first fraction you collected and add it to a 500ml separatory funnel. Dilute it with about the same volume of distilled water and shake. Let the layers separate and drain the bottom (aqueous) layer. Add the rest of the distillate you collected (with a very obvious difference in layers) and dilute with enough water to fill the funnel up. Drain off the lower (aqueous) layer, saving the benzaldehyde. If you used ethanol, wash the benzaldehyde a few times with plain distilled water. Be conservative on the water you use though, because benzaldehye is a little soluble in pure water. If you used acetic acid, you must neutralize the benzaldehyde by washing it a few times with dilute sodium (bi)carbonate solution and distilled water. Clearly, it is much more beneficial to use the ethanol solution as opposed to the acetic acid solution. Once the benzaldehyde has been washed/neutralized, dry it with magnesium sulfate. It should be a clear yellow to clear orange liquid now. Distill the benzaldehyde under reduced pressure to minimize decomposition. Use a monograph to predict the boiling point of the pure benzaldehyde. You can also distill it under atmospheric pressure, but expect slight decomposition. Collect the portion coming over between 178-180C. Theoretical yield is 29.4g. Last time I attempted this, I obtained ~22g which is about a 75% yield; 70% yields are standard for this procedure.
Into a 1000ml flask, add 45g of hexamine. Prepare either a 60% ethanol solution by mixing 80ml of ethanol in 55ml of distilled water, or a 50% acetic acid solution by mixing 80ml glacial acetic acid with 80ml of distilled water. Swirl the flask at least enough to dissolve all visible solids - it doesn't have to become a completely clear solution, you just don't want a cake of hexamine at the bottom. Add 35ml of benzyl chloride to the flask and fit the reflux column to the flask. If you used ethanol, you can use a water bath, otherwise, use an oil bath to heat it to reflux and hold it there for about two hours. Prepare a ~10% solution of hydrochloric acid by mixing 20ml of 31.45% with 40ml of distilled water, or 30ml of 20% with 30ml of distilled water. After the materials in the flask have refluxed for two hours, add the above solution of hydrochloric acid to it and continue refluxing for at least 15-20min. After this, remove the flask from the bath and let it cool to room temp. You should see two layers, the bottom layer is usually a light orange and the top layer can be yellow to orange. The top layer is your benzaldehyde.
Set the flask up for simple distillation and begin heating it on an oil bath. You will now be steam distilling the benzaldehyde from the reaction mixture/by products. After many tests, I have found this to be the most efficient (and easiest method) to obtain the benzaldehyde. If you used ethanol, collect the first fraction all the way up to ~98C. Now, collect everything else distilling over (whether you used ethanol or acetic acid) until the distillate is running out is mostly clear and benzaldehyde free. You may need to add more water to the distillation flask to aid in the steam distillation.
If you used ethanol, take the first fraction you collected and add it to a 500ml separatory funnel. Dilute it with about the same volume of distilled water and shake. Let the layers separate and drain the bottom (aqueous) layer. Add the rest of the distillate you collected (with a very obvious difference in layers) and dilute with enough water to fill the funnel up. Drain off the lower (aqueous) layer, saving the benzaldehyde. If you used ethanol, wash the benzaldehyde a few times with plain distilled water. Be conservative on the water you use though, because benzaldehye is a little soluble in pure water. If you used acetic acid, you must neutralize the benzaldehyde by washing it a few times with dilute sodium (bi)carbonate solution and distilled water. Clearly, it is much more beneficial to use the ethanol solution as opposed to the acetic acid solution. Once the benzaldehyde has been washed/neutralized, dry it with magnesium sulfate. It should be a clear yellow to clear orange liquid now. Distill the benzaldehyde under reduced pressure to minimize decomposition. Use a monograph to predict the boiling point of the pure benzaldehyde. You can also distill it under atmospheric pressure, but expect slight decomposition. Collect the portion coming over between 178-180C. Theoretical yield is 29.4g. Last time I attempted this, I obtained ~22g which is about a 75% yield; 70% yields are standard for this procedure.