Modafinil (CAS 68693-11-8) — molecular structure, sulfinyl stereocentre and synthesis route from benzhydrol

Modafinil is a crystalline organic reagent classified among the diphenylmethylsulfinylacetamide derivatives — a small family in which a rigid benzhydryl unit is tied through an oxidised sulfur atom to a short amide arm. CAS number 68693-11-8, molecular formula C₁₅H₁₅NO₂S, molar mass 273.35 g/mol. What follows covers the physicochemical behaviour of the material and the way it is handled on the bench, nothing else.

Molecular skeleton and functional groups

The structure reads most easily as three modules. The first is the benzhydryl unit: two phenyl rings mounted on a shared methine carbon, forming a bulky non-polar surface. The second is the sulfinyl bridge — sulfur at an intermediate oxidation state, carrying a short and strongly polarised S=O bond. The third is an acetamide arm terminating in a primary amide that supplies both a hydrogen-bond donor (N–H) and an acceptor (C=O).

Sulfur in the sulfinyl group carries four distinct environments: two substituents, oxygen and a lone electron pair. It is therefore a stereogenic centre of pyramidal geometry, and technical material is a racemic mixture; the resolved single enantiomer travels under a separate name in the literature. Pairing a strongly polar sulfoxide and an amide with two aromatic rings produces a markedly two-faced molecule — a dense hydrogen-bond network in the crystal coexists with an extensive non-polar region, which explains a high melting point alongside poor miscibility with water.

Chemical class and related compounds

• the corresponding sulfide — a lower oxidation state of sulfur, both a synthetic intermediate and a process impurity,
• the corresponding sulfone — the product of over-oxidation of the sulfur bridge,
• the carboxylic analogue — formed when the amide bond is cleaved,
• adrafinil — an N-hydroxy analogue built on the same scaffold,
• armodafinil — a single enantiomer isolated from the racemate,
• FL-Modafinil (CAS 90280-13-0) — an analogue carrying two fluorine atoms in the para positions,
• benzhydrol and (benzhydrylthio)acetic acid — building blocks of the same structural family.

Synthetic approaches described in the literature

1. Activation of benzhydrol under acidic conditions, generating a resonance-stabilised benzhydryl cation.
2. Capture of that cation by a sulfur nucleophile, most often thioglycolic acid, giving a thioether with a free carboxyl function.
3. Conversion of the carboxyl function into a primary amide, usually through an ester or an acid chloride followed by ammonolysis.
4. Controlled oxidation of the thioether to the sulfoxide. This step governs product purity: an excess of oxidant drives sulfur further to the sulfone, which is awkward to remove later.
5. Purification by crystallisation. The order of the last two steps is sometimes reversed in the literature, and separating the enantiomers calls for a chiral stationary phase or crystallisation of diastereomeric salts.

The description is intentionally qualitative; process parameters vary between publications and are not quoted here.

Stability, degradation and influencing factors

Solubility and preparation of working solutions

The material is described as practically insoluble in water and moderately soluble in organic solvents of medium polarity such as methanol or acetone, with dimethyl sulfoxide serving as the most convenient carrier for a stock solution. On the bench the stock is prepared in an aprotic solvent with brief ultrasonic assistance and only then diluted into the target medium. See also our reagent grade material: Mebicar / Mebikar / Temgicoluril – 30x kapsułki 100m.

Moving into aqueous systems invites precipitation: the mixture should be inspected in side lighting, and quantitative work calls for syringe filtration so that suspended particles do not distort absorbance readings. Glass vessels are preferable to plastic ones, because lipophilic molecules adsorb readily onto polymer walls. Stock solutions are kept closed, cold, and away from repeated freeze–thaw cycles. See also our catalogue item: PRL-8-53, 1000mg czystej substancji ≥ 99%..

Spectral characteristics

Infrared spectra reveal the amide bands — N–H and carbonyl stretches — together with an S=O stretch lying in the range typical of sulfoxides; its position relative to sulfone bands serves as a quick check of the sulfur oxidation state. In proton nuclear magnetic resonance the diagnostic features are a single methine signal from the benzhydryl unit, a complex aromatic multiplet, and an AB pattern arising from the diastereotopic methylene protons next to the stereogenic sulfur. Amide protons give broad signals that vanish on addition of deuterated water.

In mass spectrometry the molecular ion tends to be weak while the persistent benzhydryl cation dominates the spectrum — a signature shared across the family. Purity control relies on liquid chromatography with ultraviolet detection based on the phenyl chromophore, and enantiomer separation on a chiral stationary phase.

Product classification

This product must not be used in humans in any form. The material is not a veterinary product. The material serves solely as a standard and reagent in HPLC and GC-MS analysis. It is neither a medicinal product nor a foodstuff.

Reagents of a similar class

• PRL-8-53, 1000mg czystej substancji ≥ 99%.
• Mebicar / Mebikar / Temgicoluril – 30x kapsułki 100mg. Czystość ≥ 99%
• VIAGRA / Tadalafil Pureza ≥ 99% 1000mg.
• Methylene Blue / BŁĘKIT METYLENOWY. Czystość ≥ 99.99% 1000mg.

Bibliography

Records indexed in PubMed for this substance; each entry is identified by its PMID.

• Sangroula D, Substance use & misuse, 2017 — PMID 28350194
• Minzenberg MJ, Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 2008 — PMID 17712350
• Pacheco RL, International journal of clinical practice, 2019 — PMID 30444561
• Repantis D, Psychopharmacology, 2021 — PMID 33201262