Supramolecular Arrangement in Styphnic Acid and Naphthalene-1,4-diol (1 : 1) through a Novel Synthetic Rote for Styphnic Acid

Abstract

The chemical preparation and crystal structure of styphnic acid and naphthalene-1,4-diol (1 : 1) (I) have been reported. The compound crystallizes in the orthorhombic system in space group Pnma and cell parameters 𝑎=6.6712(2), 𝑏=16.8267(7), 𝑐=13.6450(5) Å and 𝑉=1531.71(10) ų, and 𝑍=4. Crystal structure has been determined and refined to 𝑅=0.0576. The crystal structure of I, the asymmetric unit, contains C₆H₂N₃O₇, C₁₀H₇O, and it is a half portion of both styphnic acid and naphthalene-1,4-diol. The O1–H1⋯O2 intramolecular hydrogen bond was found between the O–H and a nitro group in the styphnic acid unit.

1. Introduction

Many of the electron donor-acceptor (EDA) interactions had been widely studied spectrophotometrically in the determination of drugs that are easy to be determined based on CT-complex formation with some electron acceptors [1–3].

The study of the charge-transfer complexes formed in the reaction of aromatic electron acceptors (π-acceptors) with various electron donors has attracted considerable interest, and growing importance owing to their significant, physical and chemical properties [4, 5]. A vast number of the charge-transfer complexes formed during the reaction of σ- and π-acceptors with organic compounds containing different sites of donation (nitrogen, oxygen or sulfur atoms) were extensively investigated [6–10]. This paper is a continuation of our previous investigation [11–14] concerned with the formation of stable charge-transfer complexes formed during the reaction of electron donors.

The picric acid (2,4,6-trinitrobenzene-1-ol) (2,4,6-trinitrophenol) and picrates can be used in explosive materials. 2,4,6-trinitrobenzene-1,3-diol is an analog of the picric acid and it is also known as styphnic acid, or trinitroresorcinol. With regard to explosive power and sensitiveness styphnic acid is similar to picric acid. Since, its price is considerably higher than that of picric acid, it is not used in explosive technology and only lead styphnate (lead trinitroresorcinate) is of great practical importance as an initiator. On the whole, the properties of styphnate salts are similar to those of picrates.

This paper describes the new synthesis route for the styphnic acid and naphtalene-1,4-diol reaction between picric acid (π-acceptor) and naphtalene-1-ol (α-naphthol) (donor) and its cocrystal structure.

2. Experimental

To a solution of α-naphthol (144 mg, 1 mmoL) in 10 mL of CH₃OH/CHCl₃ 50/50 w/w, a solution of picric acid (229 mg, 1 mmoL) in CH₃OH (25 mL) was added at room temperature. An orange red color developed and the solution was allowed to evaporate slowly at room temperature. Orange red crystals were formed, filtered off, and dried under vacuum. IR (KBr): (3444 and 3294 cm⁻¹), (1577, 1543, and 1516 cm⁻¹), and 1343 cm⁻¹ for 𝜈(OH), 𝜈_as(NO₃), and 𝜈_s(NO₃), respectively. ¹H NMR (DMSO-d₆): δ = 6.91 (s, 2H, H₂ and H₃, naphthalene ring), 7.45 (dd, 2H, H₆ and H₇, naphthalene ring), δ = 6.82 (d, 2H, J = 2.20 Hz, H₅ and H₈, naphthalene ring), 8.17 (s, 2H, 2OH, naphthalene ring), 8.64 (s, 1H, styphnic acid proton), and 9.31 (s, 2H, 2OH, styphnic acid OH). MS m/z = M⁺ (405), 389, 245, 229, 199, and 144 (Scheme 1).

Scheme 1 

3. Results and Discussion

It is well known that nitro group in picric acid is a strong oxidizing agent, and concerning picric acid that contains three of these nitro groups, we believed that, it is the source of the oxidation of the α-naphthol along with itself to give naphtalene-1,4-diol and styphnic acid, respectively. Similar features of this kind of mechanisms were suggested earlier [15]. The reaction under investigation is a reaction between an electron-rich α-naphthol and electron-poor picric acid in a methanol chloroform mixture as a solvent.

The ¹H NMR of the separated complex (Figure 1) revealed one singlet signal for the symmetrical H₂ and H₃ protons in 1,4-dihydroxynaphthalene at δ = 6.91 ppm along with one singlet signal for one proton in styphnic acid at 𝛿 = 6.91 ppm.

Figure 1 

1H NMR spectrum of naphtalene-1,4-diol and styphnic acid complex.

The mass spectra (Figure 2) showed m/e fragmentations 405, 389, 245, 229, 199, and 144; the fragment expected for these fragmentations are as follows.

(a)

(b)

(c)

Figure 2 

Mass spectrum of naphtalene-1,4-diol and styphnic acid complex.

The IR spectrum (Figure 3) showed bands at (3444 and 3294 cm⁻¹), (1577, 1543 and 1516 cm⁻¹), and 1343 cm⁻¹ assigned to 𝜈(OH), 𝜈_as(NO₂), and 𝜈_s(NO₂), respectively.

Figure 3 

Infrared spectrum of naphtalene-1,4-diol and styphnic acid complex.

In the crystal structure of I, the asymmetric unit, contains C₆H₂N₃O₇, C₁₀H₇O, and it is a half of portion of both styphnic acid and naphtalene-1,4-diol. The O1–H1⋯O2 intramolecular hydrogen bond was found between the O–H and a nitro group in the styphnic acid unit (Figure 4, Table 1).

Table 1 

Crystal data and structure refinement for the compound.

Figure 4 

The asymmetric unit of the compound with the atomic labeling scheme. Displacement ellipsoids of non-H atoms are drawn at the 30% probability level.

The possibility of hydrogen bonds was explored for the synthesized compound by the statistical criterion proposed by Taylor and Kennard [15] and was found to be very effective in supramolecular arrangement of molecular units in the solid state. In the solid state, the naphtalene-1,4-diol part of the asymmetric unit acts as hydrogen bond donor via its O5, C5, C8, and C9 atoms to O2, O3, and O4 atoms of symmetry related styphnic acid parts which are explained below, to give three-dimensional network in supramolecular arrangement.

Along the 𝑎 axis, naphtalene-1,4-diol form infinite polymeric chains by C5–H5⋯O2ⁱⁱ at 𝑥+1/2, 𝑦, −𝑧+1/2 and C9–H9⋯O4ⁱⁱⁱ, at 𝑥−1/2, 𝑦, −𝑧+1/2 hydrogen bonds (Figure 5, Table 1).

Figure 5 

The view of infinite polymeric chains along the 𝑎 axis. Also, C8–H8⋯O1iv and C9–H9⋯O3iv at −𝑥, −𝑦+1, −𝑧+1 intermolecular hydrogen bonds form infinite polymeric chain along the  𝑏 axis (Figure 6, Table 1).

Figure 6 

The view of infinite polymeric chains along the 𝑏 axis.

These two polymeric chains fit into one another by molecules in asymmetric unit so the polymeric chains are arranged approximately perpendicular to each other (Figure 7).

Figure 7 

The arrangement of polymeric chains along 𝑎 and 𝑏 axis.

The naphtalene-1,4-diol in the asymmetric unit bonds to styphnic acid at −𝑥+1/2, −𝑦+1, 𝑧+1/2 by the O5–H5O⋯O4^v and C5–H5⋯O3^v intermolecular hydrogen bonds to form polymeric chains lying parallel to the [010] plane (Figure 8, Table 2).

Table 2 

Selected interatomic distances, angles, and hydrogen bond geometries (Å, °).

Figure 8 

Forming of polymeric chains lying parallel to the [010] plane.

The C5 and C9 atoms of naphtalene-1,4-diol in the asymmetric unit act as bifurcated hydrogen bond donors via their H5 and H9 either to form polymeric chains along the 𝑏 and 𝑎 axes or to extend the these chains through the 𝑐 axis so the polymeric chains bond to each other by O2ⁱⁱ⋯H5⋯O3^v and O3^iv⋯H9⋯O4ⁱⁱⁱ bifurcated hydrogen bonds, respectively (Figure 9, Table 2).

Figure 9 

The view of bifurcated hydrogen bonds.

Also, there were found some 𝜋⋅⋅⋅𝜋 interactions between the rings of naphtalene-1,4-diol and the rings of styphnic acid through the 𝑐 axis (Figure 10) to contribute to supramolecular arrangement in the solid state (Figure 11).

Figure 10 

The 𝜋⋯𝜋 interactions in the molecules along the 𝑐 axis.

Figure 11 

A packing diagram of the molecules; the 𝜋⋯𝜋 interaction was omitted for clarity.