Comparatively Speaking: Compounds vs. Compositions

Small pouring beaker
Small pouring beaker

Formulating is more complicated than what students in college envision it to be. In the industrial laboratory, formulators deal with raw materials that are the product of an industrial process, whereas at universities, students discuss pure chemicals. The difference between a compound and a composition has a dramatic effect upon the ability to formulate. The vast majority of raw materials used in formulations are not compounds, but rather complex mixtures called compositions.

Compounds are single chemical entities. Two examples are sodium chloride and glucose. These materials cannot be separated into components using analytical techniques. The preparation of a 1% solution of these materials using pure water and pure compound is generally not a challenge.

However, the preparation of more complex formulations based on raw materials is far more complicated and challenging, especially if the formulator wants to match viscosity, color, odor and aesthetics in products made using raw materials that are compositions. Compositions are mixtures of materials rather than single compounds. These raw materials are complex and do vary from time to time, making the compositions difficult to analyze. Raw materials can be compositions for the following reasons.

Starting materials: The materials used in the preparation of compositions are compositions themselves. For example, coconut oil is a mixture of a variety of carbon chain lengths ranging from C12 to C20.
Oligomerization: The raw materials are made through a process that provides an oligomer distribution of compounds rather than a single compound (like ethoxylation).
Residual reactants: The raw materials are not used in stoichiometric ratios, leaving an excess of one raw material present after the reaction is complete. For example, alkanolamides run with an excess of amine.
Byproducts: Some byproducts are produced during the reaction, i.e. chlorosulfonic sulfation. 
Process aids: Additives are placed in the product as processing aids to alter viscosity, or change salt response in a formulation.
Property enhancers: Bleaches, antioxidants or related materials are added to improve appearance, odor and overall acceptability.
Preservatives: Many raw materials contain antimicrobial agents that themselves are mixtures.
Solvents: Solvents are added for ease of handling or ease of making the product.

The ability to use one material as a replacement for another in a formulation requires an understanding of all these issues, making substitution difficult under many conditions. Certainly, one cannot rely upon INCI names for anything other than their intended use, namely providing label names. It is amazing how many compounds are present in the compositions that formulators purchase.

An example of a compound is lauryl alcohol (100%), which is one material that has single molecular weight, single molecular structure and a sharp melting point. However, in the composition sodium laureth 3 sulfate, the following compounds are present:

-Starting materials (from fatty alcohol, if derived from coconut): C10, C12, C14

-Oligomerization (from ethoxylation process): 0 mole sulfate, 1 mole sulfate, 2 mole sulfate, 3 mole sulfate, 4 mole sulfate, 5 mole sulfate, 6 mole sulfate

At this point, there are 21 potential different compounds that have the composition including: C10 - 0 Mole EO sulfate, C10- 1 Mole EO sulfate, C10- 2 Mole EO sulfate, C10- 3 Mole EO sulfate, C10- 4 Mole EO sulfate, C10- 5 Mole EO sulfate, C10- 6 Mole EO sulfate, C12 - 0 Mole EO sulfate, C12- 1 Mole EO sulfate, C12- 2 Mole EO sulfate, C12- 3 Mole EO sulfate, C12- 4 Mole EO sulfate, C12- 5 Mole EO sulfate, C12- 6 Mole EO sulfate, C14 - 0 Mole EO sulfate, C14- 1 Mole EO sulfate, C14- 2 Mole EO sulfate, C14- 3 Mole EO sulfate, C14- 4 Mole EO sulfate, C14- 5 Mole EO sulfate and C14- 6 Mole EO sulfate.

Since the sulfation process is not quantative, there is always a certain concentration of unsulfated alcohol present, referred to as unsulfated matter (US). The following materials possible in the United States in sodium laureth 3 sulfate are: C10 - 0 EO alcohol, C10- 1 EO alcohol, C10- 2 EO alcohol, C10- 3 EO alcohol, C10- 4 EO alcohol, C10- 5 EO alcohol, C10- 6 EO alcohol, C12 - 0 EO alcohol, C12- 1 EO alcohol, C12- 2 EO alcohol, C12- 3 EO alcohol, C12- 4 EO alcohol, C12- 5 EO alcohol, C12- 6 EO alcohol, C14 - 0 EO alcohol, C14- 1 EO alcohol, C14- 2 EO alcohol, C14- 3 EO alcohol, C14- 4 EO alcohol, C14- 5 EO alcohol and C14- 6 EO alcohol.

The total number of compounds in sodium laureth 3 sulfate is now at 42. Byproducts can include the inorganic salts sodium chloride or sodium sulfate, which brings the total compounds to 44. Solvents for sodium laureth 3 sulfate can include water and alcohol, bringing the total to 46 compounds. Finally, sodium laureth 3 sulfate can include process aides such as PEGs, property enhancers such as peroxide and hypochlorite and preservatives in mixture form.

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