Solubility of Ethyl butylacetylaminopropionate in Oil-Based Systems

Ethyl butylacetylaminopropionate (IR3535) has a mixed solubility profile due to its moderate polarity (Log P ~1.7). While it is often marketed for its water-solubility (up to 5%), it is not a purely lipophilic (oil-loving) substance.

Solubility in Coco-Caprylate/Caprate

In a base consisting mostly of CocoSilk™ (Coco-Caprylate/Caprate), the solubility of IR3535 is likely to be limited or borderline, especially at the functional concentrations required for insect repellency (typically 7–20%).

• Polarity Match: Coco-Caprylate/Caprate is a medium-polarity to non-polar ester. IR3535 requires a more polar environment to remain fully stable and clear in a formulation.
• Risk: Using Coco-Caprylate/Caprate as the sole solvent for high loads of IR3535 may result in a hazy solution, phase separation, or "dropout" (crystallization) at lower temperatures.

Recommendations for a Clear Dry Oil Spray

To create a stable, clear dry oil spray, it is recommended to use a coupling agent (co-solvent) that has higher polarity but still maintains a "dry" skin feel.

1. Isopropyl Myristate (IPM): This is the most effective co-solvent for IR3535. Technical data shows that IR3535 is soluble in IPM up to approximately 50%. It provides a very light, dry feel that complements Coco-Caprylate/Caprate.
2. LipidSoft™ C1215 (C12-15 Alkyl Benzoate): A high-polarity ester that is excellent for solubilizing active ingredients while providing a non-greasy, silky finish.
3. LipidSoft™ SPF: This blend contains Propylene Glycol Dicaprylate/Dicaprate, which is a highly effective solvent for organic actives and helps maintain clarity in oil-based systems.

Suggested Formulation Strategy

If you wish to maintain the dry feel of CocoSilk™, try the following approach:

• Primary Solvent/Coupler: Use Isopropyl Myristate or LipidSoft™ C1215 at a 1:1 or 2:1 ratio relative to the amount of IR3535.
• Base/Sensory Modifier: Use CocoSilk™ (Coco-Caprylate/Caprate) to make up the remainder of the formula to achieve the desired "dry oil" spreading characteristics.
• Ethanol (Optional): If your formulation allows, adding a small percentage of Ethanol can significantly boost the solubility and clarity of the system.

Usage Note: Always perform a stability test (including a cold-storage check at 5°C) to ensure the IR3535 does not precipitate out of the oil blend over time.