Does this reaction require catalyst/solvent?

Question

Planning on synthesising 2-formylphenyl benzoate by reacting benzoyl chloride with salicylaldehyde. Since both Benzoyl chloride and salicylaldehyde is liquid, will it require a catalyst/ solvent? Or do I just add them both in a conical flask and let a magnetic stirrer do the job?

Answer 1

Phenols react with aromatic acid chloride in the presence of a base such as $\ce{NaOH}$ at room temperature. Such reactions are called Schotten-Baumann type reactions (Ref.1&2; both are in German).

The Schotten-Baumann reaction is an organic reaction used to convert an acyl halide or anhydride to an amide, if reacted with an amine and base, or an ester, if reacted with an alcohol and base. The reaction with the amine begins with the nitrogen attacking the carbonyl carbon of the acyl halide which rearranges to kick out the halide. Deprotonation with the base then provides the final amide product. The reaction with the alcohol would happen in a similar fashion to give an ester.

Thus, as an example, you can follow the following procedure: Dissolve phenol in 5-10% aqueous sodium hydroxide solution (choose the percentage to have alkaline solution at the end) and add benzoyl chloride. Stir the mixture until the smell of benzoyl chloride has disappeared (warm if necessary). The resultant phenyl benzoate can be separated solvent extraction (ethyl acetate/water), washed with saturated bicarbonate solution followed by cold water. Then, dry organic layer and concentrate by rotary evaporation under reduced pressure to yield crude product.

Alternatively, if you preferred to do the reaction under solvent-free conditions you may follow the procedure given in Ref.3 using same starting materials. The abstract of the reference states that:

An efficient solid-phase benzoylation of phenols and alcohols was developed under microwave irradiation. A stoichiometric amount of benzoyl chloride was sufficient to carry out the reaction. This benzoylation features short reaction time, good yields, and easy workup procedures. Furthermore, the scope of the reaction was extended to prepare 3,5-dinitrobenzoyl derivatives of alcohols.

They have prepared 2-formylphenyl benzoate by this method and presented following spectroscopic data:

Liq. White oil, 85% yield. UV $\lambda_\mathrm{max}: \pu{265 nm}$. IR ($\ce{KBr}, \nu_\mathrm{max}, \pu{cm^{-1}}$): 3339, 3010, 2843, 2734, 1733, 1698, 1688, 1589, 1547. $\mathrm{^1H~NMR}$ ($\ce{CDCl3}, \pu{500 MHz}$) $\delta$ 6.97-7.02 (q, 1H), 7.25 (d, J 8 Hz, 1H), 7.34 (t, 1H), 7.41-7.55 (m, 1H), 7.62-7.69 (m, 2H), 7.94–7.96 (dd, J 1.5 Hz, J 1.5 Hz, 1H), 8.23 (d, J 8 Hz, 2H), 10.22 (s, 1H). $\mathrm{^{13}C~NMR}$ ($\ce{CDCl3}, \pu{125 MHz}$) $\delta$ 119.8, 120.7, 123.6, 126.5, 128.7, 130.2, 133.7, 135.3, 137.0, 152.3, 161.6, 165.0, 188.4, 196.6. HRMS: m/z calcd. for $\ce{C14H10O3}$: 227.0705 (M + H); found 227.0708.0.

---

References:

1. C. Schotten, “Ueber die Oxydation des Piperidins,” Ber. Dtsch. Chem. Ges. 1884, 17(2), 2544–2547 (https://doi.org/10.1002/cber.188401702178).
2. E. Baumann, “Ueber eine einfache Methode der Darstellung von Benzoësäureäthern,” Ber. Dtsch. Chem. Ges. 1886, 19(2), 3218–3222 (https://doi.org/10.1002/cber.188601902348).
3. S. Chakraborty, A. Saha, K. Basu, C. Saha, “Solid-Phase Benzoylation of Phenols and Alcohols in Microwave Reactor: An Ecofriendly Protocol,” Synthetic Communications 2015, 45(20), 2331–2343 (https://www.tandfonline.com/doi/abs/10.1080/00397911.2015.1078899).

Answer 2

Just three points why omitting a solvent might not be a good idea without experimental evidence that support the contrary:

• There is a reason many organic syntheses are run with reagents in a concentration in range of 0.1 to 1 mol/L; to moderate both rate (kinetics) and heat (thermodynamics) of a reaction. The omission of a solvent for an already exothermic reaction may lead to a "runaway", where the heat suddenly generated transforms your products into a tar. The issue regarding the heat balance often becomes important when scaling the reaction to larger batches in process chemistry.

• Secondly, your product target equally is an aldehyde. At least potentially there already is a problem (chemoselectivity) discerning one of the starting materials (salicylic aldehyde) from your product (2-formylphenyl benzoate) in respect to benzoyl chloride. In case of a highly concentrated (neat) reaction lacking any solvent, if the reaction of the acyl chloride with the aldehyde is exothermic, you may reach a temperature of your reaction mixture so elevated that both reaction pathways became accessible instead of only one (and other not envisioned here, too).

• According to the information about who sells this pricy commercial product at PubChem and how -- per gramm, instead of per millilitre -- it appears safe to assume that the product of your reaction is a solid. Having a solvent dissolving both your starting materials as well as your product equally may offer you a reaction more complete, because the progress of the reaction is not hampered by an interface of a liquid phase (your starting materials) and a solid (your product). It equally may lead you to a product more clean, since these grains won't contain (this much) of starting materials (occlusion).