4-Chloro-3-sulphamoylbenzoic acid is supplied as a white to off-white crystalline powder for pharmaceutical formulation work in tablet, capsule, granule, and injectable dosage forms, covering both oral and injectable administration. The substance is identified by CAS 1205-30-7, molecular formula C7H6ClNO4S, and relative molecular mass 235.64 g/mol. The substitution pattern—a chlorine at the para position relative to the carboxylic acid group and a sulphamoyl group at the meta position—distinguishes the molecule from non-chlorinated benzoic acid derivatives and from 4-chloro-3-nitrobenzoic acid. No current Ph.Eur., USP, or JP monograph defines this free acid as a standalone active pharmaceutical ingredient; the designation “pharma grade” therefore depends on GMP manufacture, validated analytical methods, and release specifications aligned with ICH Q6A.

Available commercial forms are generally differentiated by particle size distribution, bulk density, and microbial or endotoxin load rather than by chemical assay alone. A non-micronised crystalline grade may be selected for wet granulation, a micronised grade for direct compression or dissolution-limited tablet and capsule formulations, and a low-endotoxin grade for injectable manufacturing. When the material is used in oral solid dosage forms, the free acid is commonly combined with microcrystalline cellulose, lactose monohydrate, croscarmellose sodium, and magnesium stearate; when it is used in injectable formulations, it is converted to a soluble salt or buffered before final filtration. Published industrial process descriptions more frequently cite the molecule as a key synthetic building block for sulphamoyl-containing diuretics than as a finished active substance; purchasers should therefore confirm whether the supplied grade is qualified as an API or as an intermediate.

The free acid is chemically distinct from the sodium salts used in injectable diuretic products. It is less hygroscopic and more stable in dry solid form, but it requires deliberate neutralisation before parenteral administration. This characteristic creates a practical boundary: solid oral dosage forms can use the free acid directly, while injectable processes must include a salt-forming or buffering step, followed by sterile filtration and clarification. Dissolution testing therefore becomes a specification-critical activity for solid dosage forms, whereas clarity, pH, and particulate control dominate the injectable release package.

What Distinguishes This Sulfamoylbenzoic Acid Derivative from Other Benzoic Acid APIs?

The molecule combines an electron-withdrawing chlorine at the para position with a sulphamoyl group at the meta position relative to the carboxyl function. This arrangement changes acid dissociation behaviour, crystalline packing, and solubility relative to unsubstituted benzoic acid, 4-chlorobenzoic acid, and 3-sulphamoylbenzoic acid. The carboxylic acid group provides a salt-forming site for injectable preparation and a reactive handle for amide coupling; the sulphamoyl group contributes polar surface area and hydrogen-bond donor/acceptor capacity, which reduce octanol-water partitioning compared with non-sulphonated analogues. In tablet and capsule development, these same properties influence dissolution, because the free acid shows faster release in neutral-to-alkaline media than in acidic media.

Compared with 4-chloro-3-nitrobenzoic acid, the sulphamoyl derivative has a different reduction hazard profile and is more directly suited to sulphonamide diuretic synthesis without a nitro reduction step. Compared with 3-sulphamoylbenzoic acid lacking the para chlorine, the 4-chloro substitution changes the steric and electronic environment at the carboxylic acid and can alter coupling rates in downstream processing. Compared with finished sulphonamide diuretics such as indapamide, metolazone, and furosemide, this compound is not a pharmacopoeial finished drug product; industrial literature generally assigns it to the intermediate stage of sulphamoyl benzamide synthesis. The product should therefore be specified on the basis of impurity suite and physical grade rather than on therapeutic category alone.

Dissolution behaviour is pH-dependent and should be evaluated in more than one medium. In 0.1 M hydrochloric acid, the free acid is only sparingly soluble; in pH 6.8 phosphate buffer, carboxylate ion formation increases wetting and dissolution rate. A two-stage dissolution method using USP <711> apparatus II at 50 rpm is commonly applied, with sampling at 15, 30, 45, and 60 minutes. This pH-dependent behaviour is not a formulation defect; it imposes a specification on immediate-release tablet development and creates a processing constraint for oral liquids and granules that may be exposed to gastric acidity.

Oral and injectable grades differ chiefly in the control of microbial and endotoxin load. Non-sterile oral-grade material is normally controlled for total aerobic microbial count and total yeast and mould count; injectable-grade material must additionally meet a low-endotoxin specification and be handled in a cleanroom. The chromatographic assay may not differ between grades, so selecting a cheaper oral-grade material for injection is not acceptable solely on assay. The low-endotoxin grade is produced under more restrictive purification and drying conditions, and the batch record should demonstrate segregation from non-sterile product.

Impurity Profiling and Analytical Control

Impurity control for this compound requires a combination of reversed-phase HPLC, headspace gas chromatography, and inductively coupled plasma mass spectrometry. Related-substance methods are typically developed on a C18 column with a low-pH phosphate or phosphate/acetonitrile mobile phase and ultraviolet detection. The method separates positional isomers, starting materials including 4-chloro-3-nitrobenzoic acid if present, and polar sulphonated by-products. Because no official monograph exists, method validation follows ICH Q2(R1) for specificity, linearity, accuracy, precision, and range. Residual solvent monitoring is particularly important when the synthetic sequence employs chlorinated solvents or amide-coupling solvents such as dichloromethane, toluene, or N,N-dimethylformamide.

All methods are validated under ICH Q2(R1). For injectable use, the batch-specific bacterial endotoxin limit is calculated from the maximum intended dose using the K/M principle rather than a fixed value; a low-endotoxin grade is released only after additional depyrogenation controls and endotoxin testing. The certificate of analysis should include the full laser diffraction curve, bulk and tapped density, residual solvent clearance, and elemental impurity statement, not a single chromatographic assay. Batch-to-batch variance is observed mainly in particle size and residual solvent content, not in chromatographic purity. Production-scale lots may vary in D50 by up to ±20% across micronisation campaigns unless mill parameters are fixed. This can affect tablet content uniformity and dissolution. Buyers should not accept a simple “meets specification” statement for particle size; the full laser diffraction curve and bulk density are required for solid oral dosage development.

When Milling and Sterility Requirements Diverge Across Dosage Forms

In tablet and capsule processing, the critical powder attributes are flow, compressibility, and dissolution. The free acid can exhibit poor flow when the crystal habit is acicular or plate-like; wet granulation in a high-shear granulator with purified water or an aqueous binder system is therefore preferred over direct compression for medium- to high-dose formulations. A fluid-bed dryer is used to achieve a loss-on-drying target established for the formulation, with inlet air temperature controlled below the softening point of the material. Micronisation is generally performed in a spiral jet mill using compressed nitrogen; milled material can become electrostatically charged and low in bulk density, so it is often sieved through a 500 µm screen and blended with colloidal silicon dioxide before encapsulation or compression. Polymorph and crystallinity are monitored by X-ray powder diffraction per USP <941> because over-milling can reduce crystallinity and change dissolution.

For capsule filling, dosator-type machines can be affected by powder cohesiveness and low bulk density. Tamping pin settings and fill weight adjustments are required when the micronised grade is used directly. A higher-density granulated intermediate generally improves capsule filling performance and content uniformity. For granule and sachet preparations, the same granulation step achieves uniform distribution, but oversized agglomerates must be removed by sieving before final packaging. Tablet compression of the free acid without granulation is possible only at low active loadings. When the active fraction is high, the blend can stick or cap; pre-compression and tapered dies on a rotary press reduce lamination. Lubrication with magnesium stearate should be limited in time because over-lubrication can retard dissolution in a pH-dependent weak acid system.

For injectable formulations, the material is dissolved in water for injection after neutralisation with sodium hydroxide solution. The pH is adjusted to a physiologically compatible range, and the solution is passed through a 0.22 µm sterilising-grade membrane. Terminal autoclaving at 121°C for 15 minutes may be applied only if forced-degradation studies show no increase in related substances; published data for this specific configuration is limited, so aseptic filtration is often the default for early-stage injectable batches. The low-endotoxin grade is depyrogenated before release, and the batch-specific endotoxin limit is derived from the maximum dose. Particulate matter is controlled according to USP <788>, and osmolality is controlled according to USP <785> after reconstitution or dilution. The sulphamoyl group can undergo hydrolysis under strongly acidic or strongly alkaline conditions; therefore pH-defined stability data are required for terminal sterilisation and long-term aqueous storage.

Storage and handling boundaries are different for oral and injectable grades. Oral-grade solid is packaged in double low-density polyethylene liners inside a fibre drum and stored at controlled room temperature. Prolonged exposure above RH 60% can increase water content and alter flow or particle size distribution through agglomeration. Injectable-grade material should be opened only in a classified area with interfaces to Grade A filling; open handling is incompatible with low-endotoxin requirements. The free acid should not be dry-mixed with strong bases or primary amines without solvent control because acid-base salt formation and localised heat release can alter the sulphamoyl group. When a change in particle size, polymorphic form, or residual solvent profile is introduced, the formulation site should repeat dissolution, content uniformity, and stability assessment because these variables affect tablet hardness, capsule fill weight, granule dispersibility, and injectable clarity.

The material is manufactured under ICH Q7 when used as an API. Stability studies follow ICH Q1A(R2) and include long-term 25°C/60% RH and accelerated 40°C/75% RH conditions unless a climatic zone requires otherwise. Change control for particle size, polymorphic form, and residual solvent profile must be communicated to the formulation site because these characteristics affect dissolution and content uniformity. Residual solvent testing follows ICH Q3C and USP <467>; elemental impurities follow ICH Q3D with a risk assessment based on the intended maximum daily dose. For injectable development, the low-endotoxin grade is released only after batch-specific endotoxin, residual solvent, and particle size data are reviewed against the intended formulation and route of administration.