Background for this classification summary
- Visit the Classification Index to see other groups.
- The summary on this page follows the classification scheme of Elsner and Hoelzer, 2016. Quantitative Survey and Structural Classification of Hydraulic Fracturing Chemicals Reported in Unconventional Gas Production. Environmental Science and Technology. 3290-3314. DOI: 10.1021/acs.est.5b02818.
- Elsner and Hoelzer’s thorough and influential article provides a wealth of chemical context about fracking materials including health and environmental implications and suggestions for deeper analysis. However, the work was based partially on a early set of FracFocus (through 2013). Subsequent years have added new materials and millions more records. To extend their analysis to the rest of the FracFocus materials, we used Google’s Gemini to assist us in assigning classifications in line with EH’s methodology.
- Analysis from a FracFocus download, Jan 2025.
- Masses are not available for all records, so reported masses below are sums of only the available masses. See documentation.
- To provide useful technical information about these chemical groups, we use generative AI tools to assist with summaries (Google’s Gemini). These tools are prompted with details of the classification scheme (by Elsner and Hoelzer, 2016) and information about reported chemicals in the group. To limit inaccuracies, we feed the resulting output to competing models (OpenAI’s ChatGPT) to check for accuracy and ambiguity. In addition, we consulted Fink, Johannes, “Petroleum Engineer’s Guide to Oil Field Chemicals and Fluids” Third Edition. (2021) Gulf Professional Publishing. 1028pp.
- Functions reported here are summarized from the FracFocus field “Purpose.” There are limitations to this data: not all chemical records have a reported purpose (the “systems approach” explicitly excludes “Purpose” values from chemical records). Furthermore, “Purpose” typically describes the product, not individual chemicals within the product. The individual ingredient may serve a chemical role in the product that is different from the reported “purpose” (for example, synthetic polymers might be labeled “proppant”, but they are not primary proppants, but rather coatings for sand grains to enhance their performance.) In general, consider these “functions” as the larger purpose played by the product that contains the ingredient.
Amides, as reported to FracFocus, are a class of organic compounds characterized by the presence of a carbonyl group (C=O) directly bonded to a nitrogen atom. This functional group, known as an amide linkage, is relatively stable and less reactive than similar groups like acid chlorides or anhydrides. 1The Amides group is subdivided into three categories:
- Amides – 23 reported chemicals
- Quaternary amidoamines – 9 reported chemicals
- Cyclic amides – 4 reported chemicals
These subgroups differentiate amides based on structural features, such as the presence of a ring or a quaternary nitrogen.
From 2014 to 2024, FracFocus published 75,500 records of amides, with a total reported mass of 95,900,000 pounds. Products containing these amides serve a variety of functions in hydraulic fracturing operations, including corrosion inhibition, friction reduction, emulsifier control, surfactant activity, biocidal action, iron control, and foam generation. The diverse roles of amides arise from their ability to interact with both polar and nonpolar substances and, in some cases, their ability to form hydrogen bonds.
Subclass: Amides
Number of reported materials: 23
The Amides subgroup within the Amides category includes compounds featuring the amide functional group (-CONH-) where the nitrogen is neither part of a ring nor a quaternary ammonium salt. Despite this structural limitation, the subgroup exhibits considerable diversity.
Commonly reported examples include:
- Simple amides, such as Acrylamide (79-06-1), a known neurotoxin and potential carcinogen used as a friction reducer, and N,N-Dimethylformamide (DMF, 68-12-2), a widely used aprotic solvent. The simplest amide, Formamide (75-12-7), is derived from formic acid.
- Fatty acid amides, such as Oleic acid diethanolamide (93-83-4) and Amides, coco, N,N-bis(hydroxyethyl) (68603-42-9), are derived from coconut oil. Also included is Amides, C8-18 and C18-unsaturated, N,N-bis(hydroxyethyl) (68155-07-7). These compounds, possessing both hydrophobic and hydrophilic character, suggest surfactant applications.
- Sulfur-containing amides, including Thiourea (62-56-6), a sulfur analog of urea where oxygen is replaced by sulfur. Additionally, Sodium bromosulfamate hydrate (1:1:x) (1004542-84-0) and Sulfamic acid (5329-14-6) are classified as sulfuric acid amides.
- Fatty acid salts, such as Fatty acids, tall-oil, compounds with diethanolamine (61790-66-7), which is listed as an amide but is chemically a salt rather than a true amide.
The diverse structures within this subgroup enable these amides to serve various functions in hydraulic fracturing, including friction reduction (Acrylamide), solvent effects (DMF), and potential surfactant activity (fatty acid amides).
Most common Amides :
| Material | Name | Records and mass |
|---|---|---|
79-06-1 | Acrylamide | 29,200 records — 13,600,000 pounds |
93-83-4 | Oleic acid diethanolamide | 13,800 records — 49,500,000 pounds |
68-12-2 | N,N-Dimethylformamide | 13,600 records — 4,000,000 pounds |
| 68603-42-9 | Amides, coco, N,N-bis(hydroxyethyl) | 8,480 records — 9,590,000 pounds |
62-56-6 | Thiourea | 1,190 records — 44,900 pounds |
75-12-7 | Formamide | 966 records — 472,000 pounds |
Subclass: quaternary amidoamines
Number of reported materials: 9
The quaternary amidoamines subgroup within the Amides category consists of compounds that combine features of both amides and quaternary ammonium salts. These molecules contain an amide linkage (-CONH-) and a positively charged nitrogen atom bonded to four organic groups. Many of the listed compounds belong to the betaine class of surfactants.
Commonly Reported Compounds:
- Betaine-type surfactants, including:
- 1-Propanaminium, N-(3-aminopropyl)-2-hydroxy-N,N-dimethyl-3-sulfo-, N-coco acyl derivs., inner salts (68139-30-0)
- 1-Propanaminium, N-(carboxymethyl)-N,N-dimethyl-3-[(1-oxooctyl)amino]-, inner salt (73772-46-0)
- Cocamidopropyl betaine (61789-40-0), a zwitterionic surfactant derived from coconut oil, featuring both a quaternary ammonium group and a carboxylate group, which contribute to its amphiphilic nature.
- N-[3-(Dimethylamino)propyl] coco amides (68140-01-2), a closely related compound that lacks the carboxylate group.
- Fatty acids, tall-oil, reaction products with diethylenetriamine, maleic anhydride, tetraethylenepentamine, and triethylenetetramine (68990-47-6), a complex reaction product.
The combination of the amide and quaternary ammonium group, often along with a long alkyl chain, enhances the surfactant properties of these compounds. As a result, they play key roles in hydraulic fracturing, particularly in emulsification, foam generation, and corrosion inhibition.
Most common quaternary amidoamines:
| Material | Name | Records and mass |
|---|---|---|
| 68139-30-0 | 1-Propanaminium, N-(3-aminopropyl)-2-hydroxy-N,N-dimethyl-3-sulfo-, N-coco acyl derivs., inner salts | 1,460 records — 4,040,000 pounds |
| 61789-40-0 | Cocamidopropyl betaine | 1,060 records — 2,710,000 pounds |
| 68140-01-2 | N-[3-(Dimethylamino)propyl] coco amides | 160 records — 3,120 pounds |
Subclass: cyclic amides
Number of reported materials: 4
The cyclic amides subgroup within the Amides category consists of compounds in which the amide functional group (-CONH-) is integrated into a ring structure. These cyclic amides are commonly known as lactams.
Commonly Reported Compounds:
- N-Methyl-2-pyrrolidone (NMP, 872-50-4) – A widely used polar aprotic solvent known for its strong solvency properties.
- 1-Dodecyl-2-pyrrolidinone (2687-96-9) – A lactam with a long alkyl chain attached to the nitrogen, giving it surfactant-like properties.
- 5,5-Dimethylhydantoin (77-71-4) and its derivative (hydroxymethyl)-5,5-dimethyl-2,4-imidazolidinedione (27636-82-4) – Hydantoin derivatives containing an imidazolidine-2,4-dione ring system.
The cyclic structure of these amides significantly influences their solvency, reactivity, and functional properties, distinguishing them from linear amides. In hydraulic fracturing fluids, they serve various roles, including as solvents or co-solvents.
Most common cyclic amides:
| Material | Name | Records and mass |
|---|---|---|
2687-96-9 | 1-Dodecyl-2-pyrrolidinone | 634 records — 535,000 pounds |
872-50-4 | N-Methyl-2-pyrrolidone | 108 records — 34,900 pounds |
| 27636-82-4 | 2,​4-​Imidazolidinedione, (hydroxymethyl)​-​5,​5-​dimethyl- | 21 records — 87,300 pounds |
77-71-4 | 5,5-Dimethylhydantoin | 21 records — 18,500 pounds |
- All molecular structure images courtesy of the US EPA, except where noted. ↩︎