2-Octanol / 2-Octanone Valorisation: A Bio Based Platform to Key Chemicals
Dr Arvind S. More
Senior Manager - Research and Development
Jayant Agro-Organics Ltd

Dr Subhash V. Udeshi
Director (Technical)
Jayant Agro-Organics Ltd

This article talks about Valorisation of 2-octanol & 2-octanone. Both of these are biobased products and can substitute petroleum derived chemicals in many applications.

New product research and development in the field of chemicals has always been linked with the sustainability issues, either, it may be related to the raw materials, or from the process point of view or to the disposal of the material. Today, we live in Chemicals/Plastic Era', and undoubtedly, we are dependent upon them. The average worldwide sale of chemicals as of 2014 was USD 3.6 trillion1 and projected to pass USD 6 trillion by 20202. The precursors for most of the chemicals available today are based on petroleum resources, however, the dwindling and volatile petroleum resources, have been forcing industries to look for bio-based raw materials and greener methods to der ive chemicals. 2-

Ethyl hexanol (2-EHA) has been one of the major ingredient for manufacturing various chemical materials. The consumption of 2-EHA estimated in 2018 is up to 4.4 million tons3. The uniqueness of 2-EHA lies in its branched structure with pendant alkyl chain, which is responsible for breaking symmetry of the molecule and aiding flexibility, hence make it ideal for manufacturing plasticisers, in making acrylate monomers, and several other additives/ chemicals which elevate the final material properties. The 2-EHA is derived from fossil fuel. It's availability is finite and prices are linked to the unpredictable petroleum market. The matter of concern is products derived from 2-EHA are price sensitive and capable of impacting business adversely .

2-Octanol (Capryl alcohol, CAS No. 123-96-6) and 2-Octanone (Methyl Hexyl ketone, CAS No. 111-13- 7) are produced through the cracking of Castor oil molecule. They are bio-based branched alcohol and ketone respectively with C8 carbon chain and have structural and chemical similarities with 2-EHA. India is having a Lion's share in worldwide Castor oil production, i.e. > 80%, assuring a secure, consistent and reasonably priced supply of 2-Octanol and 2-Octanone.

2-Octanol/2-Octanone represents an ideal and in some cases better alternative to 2-EHA and its derivatives and even to n-Octanol. 2-Octanol in addition to its being substitute to 2-EHA has also its distinguishing specific properties. 2-Octanol and 2-Octanone are already serving or have potential as chemical intermediates to manufacture plasticisers, ester, diesters, polyketones, ethoxylated and propoxylated products, surfactants, antioxidants, etc. 2-Octanol and 2-Octanone are also commercially being used as solvents for applications in coatings, inks, adhesives and possibilities in fine chemicals manufacturing. Their good solvency properties (Hansen Solubility Parameter: 20.02

MPa1/2 and 17.17 Mpa1/2), reasonable volatility combined with their safe use (Flash point: >76oC) and low water solubility make them an ideal green solvent. Moreover, 2-Octanol has a low superficial tension making it applicable as a good wetting and defoaming additive. 2-Octanol and 2 -Octanone are also used as ingredients in niche flavours and fragrances.

The objective of this article is to present some of the key product folios based on 2-Octanol and 2- Octanone which are being commercially used and have potential. Scheme 1, presents, chemical valorisation of 2-Octanol & 2 -Octanone.

Plasticisers: The main usage of 2-EHA is in the production of phthalate plasticisers (DOP) and it accounts for more than 2/3 of the worldwide 2-EHA production. The success of DOP based on 2-EHA lies in its branched structure and pendant alkyl chain. When incorporated in polymer matrix, such as in PVC , it acts as spacer in polymer chains and thus increases the free volume thereby making it processable without influencing the core properties of the polymer. 2-Octanol being a branched alcohol with pendant C8 chain has now been commercialised to manufacture dicapryl phthalate (b) and other specialty esters such as, adipates(a), sebacates (a), maleates, succinates, etc. The replacement of 2-EHA with 2-Octanol made the product more sustainable with similar plasticization properties. 2-Octanol has also been utilised in the preparation of acetates (c), capryl benzoates (d), mono -carbonates(e) and dicarbonates (f), which are used as co-plasticisers in chemical industry.

(Figure 1) Scheme 1:Chemical valorisation of 2-Octanol/ 2 -Octanone

Surfactants:Surfactants have occupied an immediate place in our day-to-day life, from household materials to construction, textile, agrochemicals, food, the list is unending. The global market for surfactants in 2017 was USD 36 billion4 and it shows its impact on human and environment . Among the several classes of surfactants, non-ionic surfactants such as alkoxylated ones and anionic surfactants such as sodium sulfonic salts, sulfosuccinates are of interest from their versatility point of view, such as low surface tension, foamability, good wetting properties.5 2-Octanol can be used to prepare disodium capryl sulfosuccinate(DSCSS) (z), dicapryl sulfosuccinate(DCSS) (y), capryl ethoxylates (u), capryl ethoxylate sulfates (x), capryl sulfate (v), capryl sulfonate (w), capryl propoxylates, capryl EOPO copolymers (t) and their sulfates, phosphates. The surfactants based on 2-Octanol have low surface tension, e.g. capryl sulfonate (w) and DC-SS (y) have a surface tension below 27 dynes/cm.

Lubricants: 2-Octanol, being a branched alcohol, opens a platform of plethora of chemicals having potential uses as lubricants. There are several examples, where 2-Octanol is being used as intermediate to prepare lubricants, such as long chain fatty esters such capryl palmitates, stearates, leates, myristates, capryl and dicapryl carbonates (f). Among that, the dialkyl carbonates such as dicapryl carbonate (f) denote newer class of lubricants. The tribological studies, suggest these carbonates to have better lubricity properties than mineral oil or traditional synthetic esters of similar viscosities. Their unique property is unlike esters, the carbonate moiety decomposes to CO2 and parent alcohol, without formation of corrosive carboxylic acid as typically obser ved in esters.6

Monomers for polymerisation: The second largest usage3 of 2-EHA, after the plasticisers, is in making 2-EHA acrylates, which are further polymerised, or in situ polymerised to use in adhesives, surface coating materials, emulsions. In a similar way, 2-capryl acrylates (k) are developed and their properties are established, like low Tg polymer giving better adhesion characteristics for use in adhesives, particularly in pressure sensitive adhesives. 2-capryl acrylates can also be used in the production of homo and copolymers such as in combination with acrylic acid and its salts, esters, amides, methacrylates, acrylonitrile, vinyl monomers, unsaturated polyesters , etc. When used in emulsion paint formulations, the polymers based on 2 -capryl acrylate will impart good water resistance, low temperature flexibility and excellent weathering and sunlight resistance, due to the hydrophobic pendant C8 chain.

Bisphenol-A is obtained by a reaction of acetone and phenol and is a very versatile monomer, used in the synthesis of polycarbonates, polyesters, epoxy resins, etc. The polymers based on bisphenol-A have their limitations, such high Tg, high melting thermal characteristics, low fluidity and processing difficulties. In order to improve the processing characteristics, incorporation of pendant alkyl chain in the bisphenol backbone has proven to be successful. The 2-Octanone can be explored to prepare bisphenol (s) with pendant alkyl C7 chain. The alkyl chain is believed to impart flexibility in the molecule and thereby to the polymer without influencing its thermal stability. Also the presence of alkyl chain breaks the molecular packing and enhance its solubility in organic solvents.

Additives for chemicals: The chemicals are composed of different types like single organic entity, oligomeric chemical products to polymers (plastic, rubber, viscous liquid, etc.). Most of the chemicals cannot be used as such and need alterations or some other chemical addition in order to have a better applicability. 2-Octanol and 2-Octanone have been successfully used in the synthesis of such additives for numerous purposes. To name a few:

2-Capryl glycidyl ether:- Epoxy resins based on bisphenol-A glycidyl ethers are very viscous and hardly facilitate the coating application without using solvents for dilution. Solvents evaporate and pollute the air besides leading to loss in material. Also the use of solvents is banned in most of the countries in resins used in food products, cosmetic products packing due to their toxicity. The 2- Octanol based glycidyl ether (g) is a colourless, low viscosity epoxide resin and used as a reactive diluent in epoxy formulations. It not only imparts substantial viscosity reduction in epoxy resins, but becomes a part of the polymer backbone and hence adds to the solids and does not contribute to the volatiles. It also has positive impact resistance properties when incorporated in the epoxy resins. Capryl glycidyl ether (g) is compatible with conventional epoxy resins and can be mixed by simply blending.

Cyclic acetal derivative of 2-Octanol: 2-Octanol when reacted with glycerine gives cyclic acetal derivative (h). These cyclic acetals are used as additives in biodiesel. They are also used as coalescing agents in emulsion paints to bring down the minimum film forming temperature of the film. Moreover, capryl based cyclic acetals when esterified should give excellent lubrication properties in combination with the parent lubricant. These acetals are also used as solvents for herbicides, agricultural formulations, as plasticiser for polymers and as emollients , etc .[7, 8]

Methyl heptyl ketoxime (MHKO):Airdrying paints and inks under storage have a tendency to form a skin due to oxidation which affects the quality and leads to loss in material. In order to overcome that, oximebased additives are used as anti-skinning agents in such paints and inks. The antiskinning additive, MHKO (i) based on 2-Octanone has shown good performance in anti-skinning behaviour when added in paints, lacquers, varnishes and in printing inks. It has good solvency and compatibility with variety of paints and varnish products. The MHKO being adequately volatile in nature, allows satisfactory drying of the paint film in stipulated duration.

The MHKO can also serve as a blocking agent for isocyanates that allows prolonged stable storage of either isocyanates or isocyanate terminated prepolymers. The MHKO (i) can also be used to prepare crosslinking agents for silicon sealants, with advantages such as fast cur ing, excellent adhesion, etc.

Amine derivatives based on 2-Octanone: 2-Octyl amine (capryl amine) (j) is a secondary amine having potential to be used in preparing phase transfer catalysts, pharmaceutical intermediates, blocking reagents and in epoxy resins, in preparation of hindered amines for water treatment as flocculants , organic acids e.g. Acetic acid scavenger leading to insolubilisation, etc .

Reaction of 2-Octanone with Aniline or p-Phenylenediamine leads to hindered amines which are used as anti-ozonant additives for rubbers or as a light stabilisers.

Alkylated phenols: 2-Octanol undergoes dehydration under acidic conditions to yield mixture of unsaturated aliphatic units, such 2 -Octene, 1-Octene. The 1-Octene is used as co-monomer with ethylene for LLDPE synthesis, whereas, 2-Octene can be reacted with phenol ring to obtain ortho and para isomers of octyl phenol (q, r). These isomers of branched alkylated phenol serve as antioxidants and stabilisers for polymers, fuels, etc. These alkylated phenols can be subjected to ethoxylation and propoxylation to obtain non-ionic surfactants to be used as alternatives to nonyl phenol ethoxylates.

The octyl phenol when reacted with aldehydes, gives phenolic resins. On copolymerising with other phenolic resins even in small proportions, it yields water resistant, soluble phenolic resins with improved electr ical properties.

Assorted usages of 2-Octanol/2-Octanone:There are several other products and applications available based on 2-Octanol and 2-Octanone, such as uses in flavours and in fragrance molecules, either directly in blends/formulations or for instance after reacting with Benzaldehyde, a fragrance popularly known as Jasmine is obtained. 2-Octanol, due to its low surface tension, is used as a defoamer in paper, oilfield, cement paints, mineral extraction and in coil coating formulation. In addition to being a chemical par t of adhesives as in form of acrylates, both products can be used as solvents in adhesive formulations. 2-Octanol is also used to extract rareearth elements, such as Tantalum, Niobium, etc. from their ores. Similarly, 2-Octanone has also demonstrated its ability as a high-boiling green solvent in coatings, inks, colorant applications. It gives, good levelling proper ties, due to reasonable evaporation rate and it also gives, anti-blushing proper ties for nitrocellulose lacquers. Moreover, unlike commonly used solvents which lead to crazing of plastics, 2-Octanol and 2 -Octanone do not lead to such crazing and thus suitable for coatings used on plastics and in electrophoretic coatings. The 2-Octanol/2-Octanone on subsequent reactions, such as oxidation with nitric acid give Hexanoic(l) and Heptanoic acids (m), which are extensively used in fragrances and in flavours. These monobasic acids also serve as precursors to derive specialty fatty esters.

In conclusion, 2-Octanol and 2-Octanone both being completely bio-based, renewable resource provide green, stable and sustainable alternatives in various applications.

References

1. http://www.essentialchemicalindustry. org/the-chemical-industry/the -chemicalindustryhtml
2. http://www.ciel.org/issue/global-chemical-safety/
3. 2-Ethylhexanol Market (2-EH) by Applications & Geography - Trends and Forecasts to 2018 - Report by MarketsAnd- Markets
4. Global Markets for Surfactant Chemicals and Materials, December 2017 - Report by Report Linker
5. Wiesław Hreczuch, Karolina Dabrowska, Arkadiusz Chrusciel, Agata Sznajdrowska, Katarzyna Materna, J. Surfact. Deterg. 2016, 19, 155.
6. James A. Kenar, Gerhard Knothe, Robert O. Dunn, Thomas W. Ryan, Andrew Matheaus, J.Am. Oil Chem. Soc, 2005, 82, 201.
7. Marcelo Eiji Borges Sato, Sao Paulo., USP 2014/0350269 A1, dated 27 November 2014.
8. Kenneth M. Doll, Sevim Z. Erhan, Green Chem., 2008, 10, 712.