Prop-2-ynyl 3-methoxy-4-(prop-2-ynyloxy)benzoate

The title compound, C14H12O4, was prepared via alkylation of 4-hydroxy-3-methoxybenzoic acid with propargyl bromide in the presence of K2CO3.


Structure description
Vanillic acid (4-hydroxy-3-methoxybenzoic acid) is an aromatic phenolic acid widely used as a flavouring agent in the food industry.4-Hydroxy-3-methoxybenzoic acid is naturally observed in some forms of vanilla and many other plant extracts, but may also be chemically synthesized (Calixto-Campos et al., 2015).In addition to being a flavourant, this compound offers remarkable therapeutic (anticancer, antiobesity, antidiabetic, antibacterial, anti-inflammatory, and antioxidant) effects (Kaur et al., 2022) and versatility for use in polymeric coatings (Silva et al., 2016;El-Toni et al., 2005), as an inclusion agent for encapsulants (Rajendiran & Jude Jenita, 2015;Hong et al., 2008) and as a construct in metallomacrocyles (Xiong et al., 2000).More recently, this compound has been reported as a promising linker precursor towards novel coordination polymers (Belay et al., 2019).In this study, the title compound, C 14 H 12 O 4 , was investigated as an intermediate toward hydroxamic acid-type linker systems and was prepared via the alkylation of 4-hydroxy-3-methoxybenzoic acid with propargyl bromide in the presence of K 2 CO 3 (Buckley et al., 2014;Hoogendoorn et al., 2011).
The title compound crystallizes in the orthorhombic Pca2 1 (Z = 8) space group resulting in two independent molecules (A and B) in the asymmetric unit (Fig. 1) with all of the bond lengths and angles falling within the normal ranges.The differences between these two molecules are observed in the allyl groups attached to the carboxylate and para-hydroxy positions of 4-hydroxy-3-methoxybenzoic acid, respectively, which display dihedral angles varying between 7.91 (13) and 25.42 (8) � out of plane with each of the benzoate rings for A and B. This observation is best illustrated by superimposing the two molecules (Fig. 2).
Non-classical intermolecular hydrogen bonding is observed in the extended structure of the title compound.These interactions (Fig. 3) are summarized in Table 1 and a packing diagram of the title compound shows the molecules linked by infinite C-H� � �O chains along the c-axis direction (Fig. 4).

Synthesis and crystallization
A solution of 4-hydroxy-3-methoxybenzoic acid (2.0 g, 11.90 mmol) was treated with K 2 CO 3 (2.50 g, 17.85 mmol) in acetone.The reaction mixture was stirred under reflux for approximately 30 minutes followed by the addition of propargyl bromide (3.0 ml, 23.8 mmol of 80 wt.% in toluene).
After stirring for 4 h, the reaction mixture was concentrated under vacuum.The residue was extracted using ethyl acetate, washed successively (water and brine) and dried over anhydrous sodium sulfate.The crude product was then recrys-tallized from the mixed solvents of dichloromethane and hexane to provide the title compound as colourless needles.150.9, 149.0, 123.4, 122.8, 112.5, 77.8, 74.8, 56.4, 55.9, 52.2.The non-classical C-H� � �O hydrogen-bonding interactions observed for the title compound, shown as dashed lines.

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.

data reports data-2
IUCrData (2024).9, x240163 Refinement.The hydrogen atoms were refined isotropically in their idealized geometrical positions while riding on their anisotropic parent atoms with U iso = 1.2U eq for the aromatic and methine protons, and U iso (H) = 1.5U eq (C) for the methyl protons, the latter groups were refined as a fixed rotor and adjusted to match the hydrogen atoms electron density from the Fourier difference map.

Figure 2
Figure 2Superimposed view of the two independent molecules in the asymmetric unit (r.m.s.deviation = 0.113 A ˚, max displacement = 0.258 A ˚).

Figure 4
Figure 4 Packing diagram showing the title compound molecules linked by infinite one-dimensional C-H� � �O chains along the c-axis direction.

Figure 1 A
Figure 1A view of the molecular structure of the title compound as two independent molecules (A and B) in the asymmetric unit, with the atom labelling.The displacement ellipsoids are drawn at the 50% probability level.

Table 2
Experimental details.