Introduction
In today’s post, I will present yet another synthesis involving an aldolic condensation between a non-enolizable aldehyde, benzaldehyde, and acetone, an enolizable ketone. The reaction is carried out with a 2:1 stochiometric ratio between the aldehyde and the ketone and leads to the double condensation adduct. The overall reaction can be represented as follows:
The procedure presented in what follows has been taken from Org. Synth. 1932, 12, 22 (DOI: 10.15227/orgsyn.012.0022).
Experimental part
In a 250 mL beaker, 5.00 g of sodium hydroxide (125 mmol, 5.0 equiv.) are dissolved in 50 mL of deionized water. After complete dissolution, 40 mL of 95% ethanol are added, and the solution is allowed to cool to room temperature. In a test tube, 5.03 g (47.4 mmol, 1.9 equiv.) of benzaldehyde and 1.45 g (24.9 mmol, 1.0 equiv.) of acetone are mixed. Half of the acetone–benzaldehyde mixture is then added to the basic solution under constant stirring. The solution quickly develops a light yellow tint and, within a couple of minutes, a substantial amount of pale yellow precipitate forms.
After 5 minutes, the remaining acetone–benzaldehyde mixture is added, and the test tube is rinsed with a few milliliters of 95% ethanol to ensure complete transfer. Throughout the addition, the temperature of the reaction mixture remains below 25 °C. The mixture is then stirred for 1.5 h, after which the product is collected by vacuum filtration using a Büchner funnel. The solid is washed three times with abundant water, transferred to a crystallizing dish, and left to dry in air for several days, followed by drying over anhydrous calcium chloride for several weeks. A final mass of 5.33 g of product is obtained, corresponding to a 96% yield.
FTIR characterization
The obtained product was analyzed by Fourier-transform infrared spectroscopy (FTIR) using an attenuated total reflectance (ATR) accessory equipped with a diamond crystal. The resulting spectrum (32 scans, 2 cm−1 resolution) closely matches the spectrum reported in the literature (SDBS No. 4394). Differences in band intensity are consistent with the different sampling techniques used (ATR vs. KBr pellet).
