Fatty Acids in Heterocyclic Synthesis . Part XVII : Synthesis of Non Ionic Surfactants Containing Piperidine , Piperazine , Imidazole Based on Thiadiazole and Microbiological Activities Evaluation

A series of novel scaffolds Thiadiazolyl Piperidine, Thiadiazolyl Piperazine, thiadiazolidine, Thiadiazolyl thiazole and Thiadiazolyl-imidazole-Thione were synthesized from cheap, available and biologically active stearic acid. 2-amino-5-heptadecyl 1,3,4-thiadiazole reacts with chloroacetyl chloride and produced 2-choloro-N-(5-heptadecyl-1,3,4-Thiadiazole-2-yl) acetamide. Which allowed to react with Piperidine, Piperazine, urea and/or Thiourea and Potassium thiocyanate, and the latest scaffolds have been synthesized, respectively, and the structures of these compounds were established by elemental analysis, MS, IR and H-NMR spectral data. The antimicrobial activities of the synthesized compounds were evaluated in-vitro against strains of gram +ve, gram −ve bacteria and fungi. Nonionic surfactant were obtained by addition of different moles of propylene oxide (3,5,7 mole) to the synthesized compounds bearing an active hydrogen. Physico-chemical and surface properties as well as biodegradability of the synthesized non-ionic surfactants were evaluated.


Introduction
1,3,4-Thiadiazole and its derivatives continue to be of great interest owing to their great pharmaceutical and industrial importance.The specific pharmaco-

Antimicrobial Activities
Screening of The antimicrobial activity of the synthesized compounds was evaluated using modified Kirby-Bauer disc diffusion technique [20] [21] [22] [23], using Mueller-Hinton agar.In 10 ml of fresh media, one hundred micro liters of the test bacteria/fungi were grown until to be approximately 108 cells/ml for bacteria and 105 cells/ml for fungi.Ampicillin and Amphotericin B were used as a standard drugs as a positive control for antibacterial and antifungal activity, International Journal of Organic Chemistry respectively.Filter discs immersed with 10 µl of solvent (distilled water, chloroform, DMSO) and used as a negative control, then a blank paper discs with a diameter of 8.0 mm were impregnated with 10 µl of the tested concentration.(100 µl) was spread onto agar plates that are relevant to the broth in which they are maintained.Standard discs of c (Antibacterial agent), Amphotericin B (Antibacterial agent)were used as positive control for antimicrobial activity, while filter discs impregnated with 10 µl of solvent (distilled water, chloroform, DMSO) were used as a negative control.Blank paper discs (Schleicher and Schuell, Spain) with a diameter of 8.0 mm were impregnated with 10 µl of the tested concentration.The obtained data on the antimicrobial activity of the compounds are shown in Table 1.

Propoxylation
Using Morgos procedure [24], 0.01 mol of the synthesized compound was stirred with 0.5 wt% KOH solution and heated to 70˚C slow stream of nitrogen.
The nitrogen stream was stopped after flushing out oxygen, then propylene oxide in different moles (3, 5 and 7 mole) was added using a syringe drop-wise with continuous stirring under reflux.The reaction was conducted for different intervals of time (1/2 -1 h).After cooling, the flask was weighed, and the average degree of propoxylation determined from increment in the mass of the reaction mixture [25].

Surface and Interfacial Tensions
Measurements of Surface and interfacial tension of 2 (a-c) -9 (a-c) were measured by International Journal of Organic Chemistry Findlay [26] with a Krüss tensiometer [27], at different concentrations (0.05 -10 −6 mol/L) of the synthesized surfactant, and at constant temperature (25˚C ± 1˚C) for the interfacial measurements, Paraffin oil and The tensiometer was calibrated using ASTM: D1331-01 method [28].

Cloud Point
The cloud point was determined by gradual heating of 1.0 wt% solution in a controlled temperature bath and the temperature at which the clear or nearly clear solution becomes turbid was recorded [29].It is a measure of the inverse solubility of a nonionic surfactants, the reproducibility of this is checked by clearing the solution again by cooling.

Wetting Time
Draves test used to measure the Wetting time [30], of the prepared surfactants by immersing a cotton fabric in a 0.1 wt% aqueous solution of the tested surfactant and measuring The sinking time in seconds.

Foaming Properties
In a volumetric cylinder, 1.0 wt% solution of the tested surfactant was checked and allowed to fall from a set height initially produced and the height of the foam is measured according the Ross Miles method [31].

Emulsion Stability
The emulsion was prepared by stirring (10 ml, 20 mml) of aqueous solution of the tested surfactant and 6 ml of light paraffin oil using magnetic stirrer.After the mixture was vigorously shaken, it was allowed to separate the emulsion and the time taken for about (9 ml) of the aqueous layer separation express the emulsion stability of the surfactant [32].

(CMC) Measurements
The critical micelle concentration (CMC) of a surfactant is the concentration at which the solution shows an abrupt change, where the surface active ions in the solution aggregates to form larger units called micelles [33].Generally, the nonionic surfactants have lower CMC values than their alternative ionic surfactants, and the value obtained as a plot of logarithm of the surfactant concentration versus the surface tension.

Effectiveness (πCMC)
Decreasing in surface tension induced by a surfactant molecule at the critical micelle concentration is the effectiveness (π CMC ) of this surfactants and this can be calculated from difference between surface tension of the pure water (γ 0 ) and the surface tension of the surfactant solution at the critical micelle concentration [34], (γ CMC ), Equation (1).International Journal of Organic Chemistry

Efficiency
The value of negative logarithm of the bulk concentration necessary to reduce surface tension by 20 mN/m is known as efficiency of the surfactant (PC 20 ) [35], and can be calculated from the following equation, Equation (2).
where T is absolute temperature in Kelvin and R is the universal gas constant 8.31 × 10 7 ergs mol −1 K −1 .

Maximum Surface Excess Γmax
Using Gibbs equation (Equation ( 3)) and values of surface and interfacial tension, the maximum surface excess Γ max can be calculated Equation (3): where δγ surface pressure in mN/m, C surfactant concentration and (δγ/δlogC) T is the slope of surface tension versus concentration curves below CMC at constant temperature [36].

Minimum Surface Area (Amin)
The average area A min (Å/mol) occupied by each surfactant molecule and adsorbed at the saturated air/water interface have been calculated easily from Γ max values using the following equation [37] [38] (Equation ( 4)).

Hydrolysis Resistance
Resistance of decomposition of surfactant molecule in aqueous solutions even under extreme PH and temperature conditions was established by surface tension measurements of that surfactant (0.1%) solution in 5% sulfuric acid or 1% sodium hydroxide at ambient temperature.

Biodegradability of the Synthesized Surfactants
Die-Away method [39] or River test was used to test the biodegradation of the synthesized nonionic surfactants in River water.In this method samples were drawn daily, filtered and the surface tension was measured using Du-Nouy tensiometer through 7 days and the biodegradation percentage D% was calculated from the following Equation ( 5).

( ) ( )
where γ t surface tension at time t, γ 0 surface tension at time zero (initial surface International Journal of Organic Chemistry tension).γ bt surface tension of the blank experiment at time t.

Antimicrobial Activities
The antimicrobial activity of the synthesized compounds (1-9) were investigated in vitro (using a modified Kirby-Bauer disc diffusion method against two bacterial strains namely, Escherichia coli (Gram-ve), and Staphylococcus aureus Gram +ve) and two fungal species namely, Aspergillus flavus and Candida albicans With Ampicilline and Amphotericin B as a positive references for antibac- terial and antifungal agents, respectively and shown in Table 1.As shown in Table 1, the synthesized compounds showed variable inhibition efficiency against the tested microorganisms.Compounds (3 -5 and 8) exhibit moderate

Nonionic Surfactants from the Synthesized Compounds
Addition of propylene oxide in different moles (3, 5 and 7 mol) to the new synthesized compounds (2 -9) produced the nonionic surfactants 2 (a-c) -9 (a-c) which elucidated via their IR and 1 H-NMR spectra.IR spectrum of these compounds showed a broad band in the region (3.500 -2.500) cm −1 and two other bands in the region of (1100 -1000) cm −1 and (950 -900) cm −1 , which attributed to (υOH) and (υC-O-C) ether linkage, respectively, in addition to the other bands reported for these compounds. 1H-NMR spectrum showed the propyleneoxy group protons as multiple signals with the chemical shift (3.5 -3.7) ppm.The physical properties of these compounds are dipped in Table 2.

Surface Active Properties
The surface active properties of the new propoxylated compounds 2 (a-c) to 9 (a-c) were evaluated in a neutral medium, and the data obtained are listed in Table 3(a), Table 3(b).

Surface and Interfacial Tensions
The ability of surfactants to lower the surface and interfacial tension make them available for large number of applications [47].As their molecules dissociate in water, they weaken the hydrogen bond by orientate themselves in-between the water molecules, which decreases the holding forces and lowers the surface and interfacial tension.The surface and Interfacial Tensions of the new synthesized surfactants increases by increasing the number of propylene oxide units (Table 3(a)), which may be attributed to increase the attractive forces and this is in accordance with the previously reported results [48].

Cloud Point
The temperature above which an aqueous solution of surfactants becomes turbid and separates into two phases is the cloud point of surfactant.It is considered effective when used near or below the cloud point, which is helping in determination of the storage stability.The cloud point depends on the chemical struc-International Journal of Organic Chemistry ture [49] [50], and it was reported that it increase with increasing the hydrophilic part [51] [52], and this is compatible with our results (Table 3(a)).

Wetting Time
In terms of wetting time, the synthesized nonionic surfactants efficiency was measured according to Draves technique.Shorter the time of surfactant to wet a piece of cotton fibre indicates the more efficiency of the surfactant as wetting agent.As shown in (Table 3), surfactants 2 (a-c) to 9 (a-c) exhibits various wetting abilities, which in general decreased with increasing the number of moles of propylene oxide, and this may be due to increasing the adhesive forces relatively to the cohesive forces [53].

Foaming Power
By lowering the surface tension, the surfactant molecule help in foam simultaneous adsorption of the surfactant molecules onto the interface between gas and liquid interface.Using the Ross Miles method, the foam power of the synthesized nonionic surfactant was measured and the data depicted in Table 3 showed that as the number of moles of propylene oxide increase, the foam height increased, which in agreement with previously reported [53] [54] [55].

Emulsion Stability
The ability of the prepared surfactant to form emulsions spread their applications, thus the emulsifying power of these surfactants was measured in term of time needed for 9 ml of the solution is presented in Table 3(a).
The data revealed that, the emulsion stability decreases as the number of propylene oxide units increased, and it is a moderate emulsifying agents.
Generally, the surfactant solubility in the oil phase decreases by increasing the hydrophilic part (head), which weaken the emulsion stability [55] [56].

CMC Measurements
CMC is an important feature of a surfactant which measures the efficiency of the prepared surfactants.Before reaching the CMC the surface tension is dramatically changed with the surfactant concentration, and after reaching the CMC, the surface tension remains relatively constant or changes with a lower slope.
Surfactants with low CMC values exhibit excellent emulsifying, wetting, solubilizing and detergency properties.As outlined in Table 3(a), Table 3(b), the measured surface tension, CMC values and the surface tension at the critical micelle concentration (γ CMC ) of compounds 2 (a-c) -9 (a-c) increased with the increasing number of moles of propylene oxide incorporated in the structures, which in agreement with the reported results [57].

Effectiveness (πCMC)
The ability of a surfactant to induce the maximum reduce in the surface tension is a measure of the effectiveness of a surfactant (π CMC ).Since the CMC represents the minimum concentration of the surfactant needed for the maximum reduction in surface tension, thus, the effectiveness (π CMC ).Can be measured from the decrease in the surface tension of the water (γ 0 ), which is induced by this surfactant at CMC. Table 3(b) showed Logically decreasing in the effectiveness of the prepared surfactants s as (γ CMC ) increased.

Efficiency (PC20)
In aqueous media, surface active compounds act by lowering the surface tension in between water molecules, so, the surfactant performance can be measured in terms of its adsorption efficiency which is known as surfactant adsorption efficiency and defined as the surfactant concentration required to produce a 20 International Journal of Organic Chemistry mN/m reduction in surface tension and denotes as PC 20 and can be calculated by Equation (2).
Increasing PC 20 , increase the adsorption of surfactant at the interface and efficiently the surface tension reduced.Accordingly, the synthesized surfactant PC 20 values are found to be decreased by increasing the number of moles of propylene oxide (Table 3(a), Table 3(b)).

Maximum Surface Excess Γmax
The excess of surfactant per unit area of surface is known as surface excess concentration which express the extent of the surfactant adsorption at the surface of the liquid.Gibbs equation, Equation (3) express the relation between surface tension and Surface excess concentration (Γ max ) and to the maximum surface concentration CMC, and efficiency [58].
The obtained data from applying Equation (3) are listed in (Table 3(b)).It showed that by increasing the number of propylene oxide units, the maximum surface excess increased and in range of 0.79 and 2.57 mol/cm 2 .

Minimum Surface Area (Amin)
The area per surfactant molecule A min at the interface air/water at the saturated surface gives us information about the packing degree and the adsorbed surfactant orientation.(Table 3(b)) represent the calculated average areas A min which exhibit a significant decrease in A min .
Values as the number of propylene oxide units increased in a significant decrease in A min .This indicates a high packing order upon increasing number of moles of propylene oxide (n).

Hydrolysis Resistance
Because of tremendous uses of surfactants in manufacture of detergents, the surfactant stability towards acid/base hydrolysis is an important factor in its utilization.The resistance of the synthesized nonionic surfactants towards acidic and alkaline hydrolysis was tested and the data obtained presented in (Table 4).
The data showed that, in acidic medium, compounds 1 (a-c) to 9 (a-c) show high stability when boiled for 30 min, but they are less stable upon boiling for 60 min.On the other hand, in alkaline medium, they affected slightly even after boiling for 60 min.thus, the synthesized nonionic surfactants would be safe to be used in detergents manufacture.

Biodegradability
Biodegradation is the destruction a chemical by metabolic activity of microorganisms.Surfactants must be susceptible to biodegradation test in order to examine their safety to environment.The biodegradation of the synthesized sur-International Journal of Organic Chemistry factants was evaluated by the conventional River Die-Away test [59] and the data listed in (Table 5).
All the synthesized nonionic surfactants seem to degrade easily as the results showed.About 40% -50% of the surfactants was biodegradable within the first day of the test, and died away through 7 days.Consequently, these surfactants are safe for human beings as well as the environment.In general, the biodegradation of the surfactants decreases by increasing the number of propylene oxide units incorporated in the structure.Additionally, the new synthesized surfactants exhibit good fastness towards alkaline/acidic media and they are susceptible to degrade within one week.In conclusion, the new synthesized thiadiazole derivatives surfactants are safe for both human beings and the environment.So, it can be recommended as wetting, moderate emulsifiers as well as cosmetics, textiles and dyes manufacture.
New thiadiazole derivatives (2 -9) have been successfully synthesized in good yield.The synthesized compounds (2 -9) exhibited high activity toward strains of G − , G + bacteria, while compound(7) showed good antifungal activity.The new nonionic surfactants bearing heterocyclic moieties were synthesized efficiently by incorporation of different moles of propylene oxide.All the synthesized nonionic surfactants revealed good surface active properties which affected by the hydrophilic part.The lower the number of propylene oxide units, the surface and interfacial synthesized nonionic surfactants tension of the synthesized surfactants is markedly changed by the change of the hydrophilic part.Consequently, the CMC and Γ max , effectiveness (π CMC ), emulsion sta-International Journal of Organic Chemistry bility, efficiency (PC 20 ) and minimum surface area (A min ) were changed.

Table 2 .
Physicochemical properties of the synthesized surfactants.

Table 3 .
Surface properties of some synthesized surfactants.
a Number of propylene oxide units

Table 4 .
Resistance of the synthesized surfactants towards acidic and alkaline hydrolysis.

Table 5 .
Biodegradability of the synthesized surfactants.Compound No. of moles a 1 st Day 2 nd Day 3 rd Day 4 th Day 5 th Day 6 th Day 7 th Day 2(a-c)