In short
Harsh bases attack fragrance materials through chemistry you already know: high pH breaks esters and damages some aldehydes, acids catalyze other changes, and oxidizers such as bleach and peroxide attack double bonds, aldehydes and more. So a material's functional groups let you predict much of the risk before testing. Prediction narrows your choices, but only a controlled test in the real base can tell you what's actually happening. You started with functional groups and oxidation.
What you will learn
- Predict likely reactions from functional groups
- Rank materials for a harsh base
- Plan a controlled stability trial
Before this lesson: Partitioning and Release in Functional Products
What attacks what
| Base condition | Attack | At risk | Often more robust |
|---|---|---|---|
| High pH (soap, some cleaners) | Hydrolysis, condensation | Esters, many aldehydes, some lactones | Ethers, hydrocarbons, some nitriles and tertiary alcohols |
| Low pH (descaler, some cleaners) | Rearrangement, hydration | Tertiary alcohols, acetals, terpenes | Certain ethers, ketones, some nitriles |
| Hypochlorite bleach | Strong oxidation and chlorination | Most perfume materials | A small, specialized palette |
| Peroxide or oxygen bleach | Oxidation | Aldehydes, phenols, unsaturated materials | Saturated ethers and some esters |
| Fermented or enzyme-rich bases | Enzymatic cleavage | Esters | Depends on enzyme |
Working it through
Take a simple line, benzyl acetate, in a high-pH soap. It's an ester, so hydrolysis would produce benzyl alcohol and acetate. You would expect the fruity-floral character to weaken, and a mild alcohol note to remain. Compare dihydromyrcenol, a tertiary alcohol with one double bond, which is widely used for robustness in functional products, though not in every base. Tetrahydrolinalool, being saturated, removes one site of attack. In this way, you can learn to read a molecule for its vulnerabilities.
Citral gives an instructive case. It's an unsaturated aldehyde, widely appreciated and readily degraded in acidic and oxidizing conditions. Lemon notes in harsh products therefore often rely on more stable alternatives. Citrus oils themselves are rich in unsaturated terpenes, and their oxidation is a concern, too.
What else may go wrong
- Color. Vanillin and indole-type materials can discolor in soap, as you found in discoloration chemistry.
- Base change. Fragrance materials may thin or thicken a product, or break an emulsion.
- Base attack. The fragrance may consume a bleach, reducing the product's own performance, a matter for a formulator.
- New odors. Reaction products can smell, sometimes bad.
- Safety. Products of reaction may have their own hazards. Do not mix hypochlorite with acids or with ammonia, and don't improvise a bleach trial at home.
Testing
A stability trial for a functional product typically compares the fragrance in the base against a retained fragrance sample, and the base without fragrance as a blank, kept under stated conditions, with odor, color, pH and viscosity recorded at intervals. Analytical checks can reveal chemical loss your nose might miss. Some of this is possible for a small maker in mild bases. For aggressive chemistry, use a laboratory, and treat the plan below as a paper exercise.
| Sample | Condition | Check at | Measure |
|---|---|---|---|
| Fragranced base | Room, dark | Set intervals | Odor, color, pH, viscosity |
| Fragranced base | Elevated temperature | Set intervals | The same |
| Fragranced base | Light exposure | Set intervals | The same |
| Unfragranced base | All of the above | Set intervals | Reference for base change |
Practical exercise: A survival prediction for one formula
- Choose one of your formulas of about 15 lines, and a target base, such as a liquid soap at high pH or a peroxide cleaner.
- For each line, identify the functional groups, and rate the risk in that base as low, medium, high or unknown.
- Find support for at least five of your ratings in a source. Say which rest only on your reasoning.
- Propose replacements for your top three risks, and note the odor cost.
- Write a test plan on paper, including blanks and what would count as failure.
You have done this well if your ratings are tied to groups, "unknown" appears where it should, and your plan has a control. Your prediction is a hypothesis, and only testing can confirm it.
Common mistakes
- Trusting a perfume formula in a harsh base. Many fine materials won't survive.
- Testing only odor. Base change matters too.
- Experimenting with bleach at home. Don't.
Safety
Do not run practical trials with hypochlorite bleach, strong acids or strong alkalis outside a suitable laboratory. Chemicals can react dangerously, and the hazards go beyond the fragrance. The exercise below is on paper.
Knowledge check
Written and reviewed by the RUŌOD Lab team. This is general education, not legal, regulatory, medical or safety advice. Example dilutions and exercises are for learning, are not validated products, and have not been safety-assessed. Completing a lesson confers no qualification. How we check these lessons.