Dimezone S

Read the back of an ILFORD paper developer bottle and you meet a name that appears nowhere else in the course’s historical literature. Multigrade and PQ Universal are both described by their maker as dimezone-s/hydroquinone developers. The sheet names the agent, and stops.

In photography

It is the P of a modern PQ paper developer. ILFORD’s own technical sheet describes MULTIGRADE as “a rapid liquid concentrate dimezone-s/hydroquinone developer suitable for the dish/tray developing of all black and white photographic papers both resin coated, RC, and traditional fibre based, FB ones”, normally used at 1+9 and at 1+14 “for greater development control and economy”. It is clean working, keeps well as a concentrate, gives a neutral image tone with most papers, is designed for 20 °C, and is not suitable for developing films. PQ UNIVERSAL is the same pairing in a more general product: another liquid concentrate dimezone-s/hydroquinone developer for all RC and FB papers at 1+9, clean working with excellent keeping properties and a slightly warm to neutral image tone, which will also dish-process ILFORD and some other technical films.

The working solution is mildly alkaline, and ILFORD publishes the figure. Its pH and specific gravity table gives MULTIGRADE at 1+9 as pH 10.45 to 10.55, specific gravity 1.022, and PQ UNIVERSAL at 1+9 as pH 10.48 to 10.58 at the same specific gravity; the phenidone-based BROMOPHEN stock sits a little lower at 10.30 to 10.50. Two developers built on different pyrazolidones and the same hydroquinone therefore work within about a fifth of a pH unit of each other, which is a measured fact and not an explanation. ILFORD adds that these figures come from controlled laboratory conditions and that users should make their own control measurements from their own fresh solutions.

It replaced phenidone, and ILFORD says nothing about why. The same sheet still describes BROMOPHEN as a phenidone–hydroquinone powder developer, so the two agents sit on one page of one manufacturer’s literature, in different products, without a word of comparison. That is the whole of the disclosure. No substitution ratio, no proportion in the formulation, no explanation of the change, and no claim that anything about the print is different because of it. This course reports the substitution and does not account for it.

What the pairing means is nonetheless established, in the class. Kendall’s 1942 Ilford patent, the document behind the P of PQ and the source set out on the phenidone page, states its object as providing a substitute for metol and gives the quantitative claim that stuck: replacing the metol in a metol–hydroquinone developer with about one fifth to one sixth of its weight of 1-phenyl-3-pyrazolidone yields a developer of similar characteristics. Dimezone S is a 1-phenylpyrazolidin-3-one with two substituents on one ring carbon, so the class behaviour — a very small quantity of pyrazolidone transforming a much larger quantity of hydroquinone — is the behaviour ILFORD’s product name asserts. Kendall’s ratio is for phenidone and this page does not transfer it, because no source gives a ratio for this molecule.

⚗The difference from phenidone, stated exactly

Phenidone is 1-phenylpyrazolidin-3-one, C₉H₁₀N₂O, relative molecular mass 162.19. Dimezone S is 4-(hydroxymethyl)-4-methyl-1-phenylpyrazolidin-3-one, C₁₁H₁₄N₂O₂, 206.24. The difference is C₂H₄O, 44.05 g/mol: a methyl group and a hydroxymethyl group, both on ring carbon 4. PubChem’s connectivity string, CC1(CN(NC1=O)C2=CC=CC=C2)CO, shows that carbon fully substituted, where phenidone’s carries two hydrogens.

That is a structural fact, read off the record, and it is where the sourcing ends. Two inferences suggest themselves and neither is made here: that the polar hydroxymethyl group is there to raise solubility, which would matter for a liquid concentrate; and that removing the hydrogens from C4 changes what the molecule does on oxidation. No source in this course’s corpus states either. The course does not guess at a mechanism, and it does not invent a reason for a manufacturer’s decision.

Properties

C₁₁H₁₄N₂O₂, relative molecular mass 206.24, CAS 13047-13-7, PubChem CID 92238. Beyond that the record is unusually bare: the physical-description heading returns the single word “Solid” from a Sigma-Aldrich safety data sheet, and the Solubility heading returns nothing at all — no water figure, no organic solvents, no temperature series. This page therefore carries no melting point, no colour and no solubility, and says so rather than borrowing phenidone’s.

Buy the right one; the names differ by a letter. The bare name dimezone resolves in PubChem to a different compound — CID 75861, 1-phenyl-4-methyl-3-pyrazolidinone, CAS 2654-57-1 — which is Dimezone without the S, an older agent with one methyl on C4 and no hydroxymethyl. Dimezone S is CAS 13047-13-7. The course pins its record by CAS registry number for exactly this reason, and any supplier’s listing should be read the same way.

Handling

The aggregated ECHA notifications give Warning, with the exclamation-mark and environmental pictograms. H302, harmful if swallowed, is unanimous among the notifiers who supplied codes; H319 is at 84.2 per cent, H315 at 80.7 and H335 at 78.9. Two minority statements are carried on this page for what they are rather than how many hold them: H317, may cause an allergic skin reaction, at 14 per cent, and H411 at 12.3 per cent. There is no harmonised CLP entry and no national scheme in the record, so this aggregate is the only classification that exists.

There is no workplace exposure limit. Neither EH40 nor the NIOSH Pocket Guide lists dimezone or any pyrazolidone the course searched for, and EH40’s paragraph 6 says the absence of a substance from the list does not indicate that it is safe. HSE’s HSG262 explains why a 14 per cent sensitisation statement still earns a glove: once a person is sensitised, tiny amounts provoke the reaction and the only remedy left is to prevent further exposure.

Why Level A. This is the rare entry where the level follows from what the reader can buy. The course never asks anyone to weigh dimezone S; it is not sold to amateurs as a powder, and every use in this course is ILFORD’s liquid concentrate diluted 1+9 or 1+14 in a tray. Level A of the course rubric admits substances “whose GHS classification is at most irritant, harmful if swallowed, or corrosive at the concentrations actually handled”, with gloves, eye protection, ventilation and dedicated utensils; H302 plus three irritation statements is exactly that description, and the Level A pinhole labs that use this developer classify on the same reasoning. The operation that would take it out of Level A is weighing the pure powder in order to compound a developer from scratch — a fine solid carrying a sensitisation statement and an environmental pictogram, which is Level B work for the same reasons as benzotriazole, and which nothing in this course requires.

⚠Safety

Gloves and eye protection when the concentrate is poured, tongs in the tray, hands washed before leaving. Do not decant into an unlabelled bottle: the concentrate looks like every other brown liquid in a darkroom and the classification on the label belongs to the mixture, not to the molecule. The product’s own safety data sheet governs, not this page.

Waste

Spent paper developer, bottled separately from stop and fixer. The reason to bottle rather than to pour is the environmental pictogram, which the aggregated notifications attach to the pure substance through H411 at 12.3 per cent, and the reason not to combine it with fixer is Kodak’s — J-300 records that developer holds negligible silver, so mixing the two recovers nothing while spoiling a stream that does carry silver. ILFORD’s guidance for United Kingdom domestic users is to bottle each waste chemical separately, label it, and take it to a Household Waste and Recycling Centre’s chemical cupboard; its fallback of flushing a small volume of dilute working solution with plenty of water is written for a dilute tray bath entering a treated sewer, not for the concentrate in the bottle. Check your local regulations, which govern and which differ.