I worked in an oil refinery for about 30 years and know a little about the subject. The first process in a refinery is crude oil distillation. The crude is separated into different streams based on boiling point. Naphtha is the stream that is produced that has a boiling range between 100 deg F. and 360 deg F. In most refineries all of this goes into gasoline. There is a reforming step specifically to increase octane. So gasoline is a naphtha product and could be used in place of naphtha with precautions. First, with great care as we all know gasoline is explosively flammable. Thus, it must be used with good ventilation and NO flame sources. Next, in the U. S., in many states at least about 10% ethanol is blended into gasoline. A sticker by the pump will indicate that. Ethanol is an alcohol, fairly similar to iso-propanol (rubbing alcohol). So if you want no alcohol you may want to avoid that. For awhile in the U.S. MTBE (an ether) was added to improve octane but it had environmental issues and is not used much anymore. Gasoline also has small amounts (usually less than 1% of additives such as detergents and anti-oxidents for engine performance. So, in short, gasoline may be the best naphtha substitute.