Perspectives of Cashew Nut Shell Liquid (CNSL) in a Pharmacotherapeutic Context

TOMY MURINGAYIL JOSEPH,1* DEBARSHI KAR MAHAPATRA,2 P. MEREENA LUKE,1 JOZEF T. HAPONIUK1 and SABU THOMAS3

Chemical Faculty, Polymers Technology Department,

Gdansk University of Technology, Gdansk - 80233, Poland,

E-mail: This email address is being protected from spam bots, you need Javascript enabled to view it (T. M. Joseph]

2 Department of Pharmaceutical Chemistry,

Dadasaheb Balpande College of Pharmacy, Nagpur,

Maharashtra - 440037, India, E-mail: This email address is being protected from spam bots, you need Javascript enabled to view it

3School of Chemical Sciences and International and Inter-University Center for Nanoscience and Nanotechnology,

Mahatma Gandhi University, Kottayam - 686560, Kerala, India,

E-mail: This email address is being protected from spam bots, you need Javascript enabled to view it

ABSTRACT

The cashew tree consists of the cashew nut fruit (which is a curved edible seed, housed in a honeycomb-like shell), the apple, leaf, and bark. The fruit consists of an outer shell, iimer shell, and the kernel. By weight, cashew nuts comprise 50% shell, 25% kernel (including testa), and 25% shell liquid. The shell of the cashew nut (Anacardium occidentale L.) contains an alkylphenolic oil named cashew nut shell liquid (CNSL) amounting to nearly 25% of the total weight of the nut. This oil is composed of anacardic acid (3-n-pentadecylsal- icylic acid), and lesser amounts of cardanol (3-n-pentadecylphenol), cardol (5-n-pentadecylresorcinol), methylcardol (2-methyl-5-»-pentadecylresor- cinol) and a small amount of polymeric material. Other components include

  • 1 -hydroxy-2-carboxy-3-pentadecyl benzene, 1 -hydroxy-2-carboxy-3-(8 pentadecenyl) benzene, 1 -hydroxy-2-carboxy-3-(8,’ 11 ’-pentadecadienyl) benzene, l-hydroxy-2-carboxy-3-(8,’ 11,’ 14’-pentadecatrienyl)benzene, 2- methyl-5-pentadecyl resorcinol, 2-methyl-5-(8’-pentadecenyl)resorcinol, 2-methyl-5-(8,’ 1Г-pentadecadienyl) resorcinol, 2-methyl-5-(8,’ 11,’ 14’- pentadecatrienyl)resorcinol, 3-pentadeca-anisole, 3-(8’-pentadecenyl) anisole, l-methoxy-3-(8,’ 11 ’-pentadecadienyl)benzene, l-methoxy-3-(8,’ ll,’14’-pentadecatrienyl)benzene, 5-pentadecyl resorcinol, 5-(8’- pentadecyl) resorcinol, 5-(8,’ir-pentadecadienyl)resorcinol, and 5-(8,’ ll,’14'-pentadecatrienyl)resorcinol. The present chapter deals with the source of production, processes, and geographical information, export/ import, and chemical composition, industrial utility, and environmental effects of CNSL in modern perspectives.
  • 6.1 INTRODUCTION

The cashew tree consists of the cashew nut (which is a curved edible seed, housed in a honeycomb-like shell), the apple, leaf, and bark. The nut consists of an outer shell, inner shell, and the kernel. The nut was too hard to digest and was later expelled with the droppings. The thickness of the cashew nutshell (CNS) is about 1/8 inch (0.32 cm). The Cashew tree is of great economic significance to Nigeria and other tropical countries due to its valuable products [1]. These products are utilized in food, medicine, chemical, and allied industries. In addition to providing shade, the cashew tree is an embellished ornamental plant that suitably controls soil erosion. Usually, it takes about 3-4 years from planting time before fruiting. Thereafter, the tree can live up to 40 years and more [2]. The cashew fruit is unusual in comparison with other tree nuts since the nut is outside the fruit. The cashew apple which is about 10 cm long is an edible false fruit, attached to the externally born nut by a stem. Its color ranges from yellow to red, fibrous in nature, veiy juicy, sweet, pungent, and high in vitamins A and C [3]. In its raw state, CNS, which is leathery in nature, contains the vesicant oily liquid. The shell is separated from the kernel by the testa which is a thin skin surrounding the kernel. The soft honeycomb matrix, in between the outer and inner shell, contains a dark brown liquid, which is known as cashew nut shell liquid (CNSL). CNSL is dark viscous oil with a characteristic smell, quite unlike other vegetable oils. It is opaque and when applied as a thin film, it is reddish-brown in color. It is immiscible with water but is miscible with most organic solvents. CNSL has germicidal and fungicidal properties. It is used traditionally as a cure for fungal attack of the feet in India [4]. The physicochemical characteristics of CNSL are depicted in Table 6.1.

TABLE 6.1 Physicochemical Characteristics of CNSL

Characteristics

Requirement

Matter insoluble in toluene (% by wt.)

1

Viscosity (cps)

550

Loss in weight on heating (% by wt.)

1

Moisture (% by wt.)

1

Ash (% by wt.)

1

Specific gravity

0.95-0.97

Iodine value

250

Polymerization time (min.)

4

SOURCE OF PRODUCTION AND PROCESSES

In the industrial processing tasks, CNSL are often produced as a waste material. CNS contains CNSL up to about 25-35 wt.% of the nutshell weight which related to the method of extraction. Thermal treatment of cashew nuts and CNSL induces the partial decarboxylation of anacardic acid, which is completed by subsequent purifying distillation [5]. The result is 90% industrial-grade cardanol oil, which is amber-yellow, with a smaller percentage of cardol and methylcardol. Crude CNSL is corrosive but becomes less so by decarboxylation and removal of H,S during the refining process. CNSL extracted by a cold-solvent process is called natural CNSL and hot-oil and/ or roasting processed CNSL is called teclmical CNSL. Although natural CNSL has more anacardic acid than cardanol, it is decarboxylated to produce anacardol which when hydrogenated yields cardanol, the chief constituent of technical CNSL (Figure 6.1) [6].

Decarboxylation and hydrogenation of natural CNSL

FIGURE 6.1 Decarboxylation and hydrogenation of natural CNSL.

Traditionally, a number of methods have been employed to extract CNSL from the nuts. Two processes are used mainly in the extraction of CNSL: hot oil process and roasting process in which CNSL oozes out from the shell. Extraction of the oil using solvents such as benzene, toluene, petroleum hydrocarbon solvents, or alcohols, or supercritical extraction of the oil using a mixture of CO, and isopropyl alcohol are the other reported techniques for extraction of CNSL [7].

By weight, cashew nuts comprise 50% shell, 25% kernel (including testa), and 25% shell liquid. The astringent shell liquid is removed prior to shelling to allow handling of the nut and prevent the liquid from damaging the nut kernel. Kernels damaged by the dark shell liquid will be discolored and may have a serious ‘off flavor.’ The CNSL is removed either by drum roasting in high temperature oil/CNSL or by steaming, and the volumes recovered differ. With drum roasting, production is 10-12% of a possible 25%. With steaming, production is 20-25%, as it is possible to use an expeller. The use of a centrifuge following drum roasting boosts recovery levels. CNSL can also be produced from shells by using the ‘cold press’ method in an extraction unit. Gloves are sometimes worn for protection in the shelling process, but more often than not, the nuts and hands are coated in ash or some other absorbent material for protection. CNSL has an economic value and can provide many phenolic compounds with far greater versatility than petrochemical phenols [8].

GEOGRAPHICAL INFORMATION

The cashew tree, native to Brazil, was introduced to Mozambique and then India in the sixteenth century by the Portuguese, as a means of controlling coastal erosion. It was spread within these countries with the aid of elephants that ate the bright cashew fruit along with the attached nut. The world production of cashew nuts is nearly 500,000 tons per year, with Brazil being the largest producer. It was not until the nineteenth century that plantations were developed and the tree then spread to a number of other countries in Africa, Asia, and Latin America. Other countries, which produce CNSL, are India and Tanzania with the potential of producing 8,000 tonnes per annum [9].

COMPOSITION OF CNSL

The earliest work published concerning the composition of cashew nut oil was by Staedeler. Since then, many researchers have investigated the constitution of the oil. Chemically, it is a mixture of several closely related organic compounds, each consisting of salicylic acid substituted with an alkyl chain. For anacardic acid, the combination of phenolic, carboxylic, and a 15-carbon alkyl side chain functional group makes it attractive in biological applications or as a synthon for the synthesis of a multitude of bioactive compounds [10].

The shell of the cashew nut (.Anacardium occidental L.) contains an alkylphenolic oil named CNSL amounting to nearly 25% of the total weight of the nut. This oil is composed of anacardic acid (3-»-pentadecylsalicylic acid), and lesser amounts of cardanol (3-//-pentadecylphenol), cardol (5-n-pentadecylresorcinol), methylcardol (2-methyl-5-?/-pentadecylres- orcinol) and a small amount of polymeric material (Figure 6.2). The long aliphatic side-chains of CNSL are saturated, mono-olefinic (8), di-olefinic (8, 11), and tri-olefinic (8,11,14) with an average value of two double bonds per molecule. A large number of chemicals and products have been developed starting from CNSL by taking advantage of the three reactive sites, namely, phenolic hydroxyl, aromatic ring, and unsaturation (s) in the alkenyl side chain [11].

A group of researchers identified the components of anacardic acid as 1 -hydroxy-2-carboxy-3-pentadecyl benzene, 1 -hydroxy-2-carboxy-3-(8’- pentadecenyl) benzene, 1 -hydroxy-2-carboxy-3-(8,’ 11 ’-pentadecadienyl)

Structure of active constituents of CNSL

FIGURE 6.2 Structure of active constituents of CNSL.

benzene, and l-hydroxy-2-carboxy-3-(8,’ll,’14’-pentadecatrienyl)benzene

[12].

In a report, the components of 2-methyl cardol as 2-methyl-5-pentadecyl resorcinol, 2-methyl-5-(8’-pentadecenyl)resorcinol, 2-methyl-5-(8,’ 1Г-

pentadecadienyl) resorcinol, and 2-methyl-5-(8,’ll,’14’-pentadecatrienyl) resorcinol have been found [13].

Researchers identified the components of cardanol as 3-pentadeca- anisole, 3-(8’-pentadecenyl)anisole, l-methoxy-3-(8,’ 11 ’-pentadecadienyl) benzene, and l-methoxy-3-(8,’ll,’14’-pentadecatrienyl)benzene. The same group of workers also identified the components of cardol as 5-pentadecyl resorcinol, 5-(8’-pentadecyl)resorcinol, 5-(8,’ 11 ’-pentadecadienyl)resor- cinol, and 5-(8,,ll,,14’-pentadecatrienyl)resorcinol [14].

INDUSTRIAL UTILITY

CNSL is a very important industrial raw material which has got multifarious uses. Considerable research work has been done on the utilization of CNSL in India and abroad. The main outlets for the utilization of CNSL and its derivatives are the brake lining industry, paint, and varnish industiy, laminated products, foundry core oil, and rubber compounding. CNSL is a versatile raw material which has many industrial applications with 200 patents [15]. There is considerable scope for its utilization in the development of diugs, antioxidants, fungicides, bactericides, insecticides, surface-active agents, etc. The main factors that are affecting the utilization of CNSL are its dark color, variable quality, and above all its high price. It is a dark brown and partially polymerized by-product, especially when derived from the most diffused roasted mechanical processing of the cashew nuts. It may represent both a dangerous source of pollutant, and a low-cost, widely available, and renewable raw material for obtaining pure cardanol useful in fine chemical processes [16]. Among the renewable resource materials, CNSL is considered as an important starting material due to its unique structural features, abundant availability, and low cost. In the search for functional materials and chemicals from renewable resources, CNS are one of the agro wastes from cashew nut processing factories, have proven to be among the most versatile bio-based renewable materials. The main uses include waterproofing, boiler fuel, laminating resin, biofuel, paint, adhesive, electrical conductor, flame retarders, foundiy chemical, automotive brake lining, insulating varnish, marine antifouling coating, epoxy resin, polyurethane (pu) polymer, topical medicine, etc. [17].

 
Source
< Prev   CONTENTS   Source   Next >