I'm stuck back in time, in the year zero, and lost in India; I need acetone, but how do I produce it? Also, I must avoid contact with people for safety reasons, so I'm living alone.
With no starting tools this is a big undertaking for your loner, but with the right skill set you could do this with the natural elements you would expect to find almost anywhere in India.
In any such suvival setting, you will first want to make some basic stone tools: an axe, a chisel and a hammer. This will involve a lot of time spent at the river or beach grinding wet stones together into sharp edges (you don't want to use napping for these tools or the edges will be too acute and serrated which will break when used on wood.) For handles, you can use either fire boring or halved, bent, and bound bamboo. These will help you both with the subsequent steps and with all the other things you will be doing to survive such as gathering fire wood, building a shelter, making traps, etc.
Once you have some basic tools and survival needs met, you will need to make a basic barrel for making alcohol in. A bamboo tube would probably be the easiest way to make one, but fire boring a log or making a clay jug would also work. Either which way you will want your stone tools to carve a wooded cap to seal it with. You can use any local grasses for the brewing so you are not cutting into your edible fruit. You will want to start soaking those early on since it will take a while to grow a decent yeast culture. Once you have your yeast culture you can start brewing some grass alcohol in the barrel. Once your have your alcohol, you will need to open up the barrel and let it breath so that it turns to vinegar.
Then you use the vinegar to dissolve something with a lot of Calcium Carbonate such as limestone, eggshells, or marble. Most natural settings in India will contain at least one of these. This reaction will form Calcium Acetate crystals.
Normally Calcium Acetate is distilled in a glass apparatus, but using clay harvested from your natural environment, you could make a similar apparatus out of ceramics. First you would make a kiln out of clay, then you would create the dry distillery out of more clay and fire the one in the other to harden it. It would be a bit of a hard shape to make, but if you do it in multiple sections, you can seal the parts together with mud when doing your distilling. At this point, it is important to keep in mind though that basic earthenware clay will not be suitable to contain the acetone. If your clay is porous, your acetone will evaporate through your container; so, to contain and store the acetone, you will need to double fire it with a second round of ash glaze. This will give your ceramics a glassy exterior with the same resilience to evaporation and corrosion as using a more modern glass solution.
The Calcium Acetate crystals you grew then need to be ground up and dry distilled which will separate the Calcium Acetate back into Calcium Carbonate and Acetone. The Acetone will be released as a gas that will gather in a top chamber, then be captured and separated through condensation.
There was no year zero. The current numbering of the years was invented in the 6th century; they had no idea of zero-based numbering in the 6th century. The year before 1 CE is counted as 1 BCE.
Historically, acetone was originally made (by Andreas Libavius, at the beginning of the 17th century) by the distillation of lead sugar (aka lead acetate). You can make lead acetate by boiling lead in vinegar.
I have no idea from where you can get lead and vinegar, and distillation apparatus, and the cauldrons to boil the lead etc. without entering into contact with people. The did not have Amazon and Ebay in the 1st century.
I'd like to build on the excellent answer from NosaJimiki, because although the first steps are pretty good, I think it goes off the rails a little with needing to reinvent the iron age. Resources needed: A forest, some stone, some clay
Step 1) Stone age tools - You will need a round, bowl shaped stone, a large, flat stone, and a sort of trough shaped stone. I'd suggest painstakingly grinding softer stones with harder stones over several weeks.
Step 2) Wooden tools - You will need a digging stick, a firebow, two long forked sticks, two short forked sticks, and two poles. These can probably be broken off trees
Step 3) Dig some pits. Line pits with clay, to keep the water in
Step 4) Gather a massive quantity of fruit: Berries, crab apples, grapes, whatever is around and that you don't want to eat.
Step 5) Mash fruit in pits. Leave to ferment in the open air
Step 6) While fruit is fermenting, raid bird's nests for eggshells. This will be messy, and may get you attacked by eagles, sparrows, hawks, etc.
Step 7) Once pits smell like vinegar, add eggshells until eggshells no longer dissolve.
Step 8) Allow water to evaporate from pits. You can gently help this along by adding warm stones from the fire
Step 9) Crystals should start to form. Save these. Dry them as much as possible
Step 10) lay out your still: Put the stone bowl where you'll build your fire. Position the flat stone above it, angled towards the stone trough.
Step 11) Start your fire, and in small batches, add the crystals. Acetone will start to evaporate off them, hit the flat stone, condense, then run into the trough. You'll want to do this a little at a time, giving the flat stone time to cool down
Then, you have (probably impure) acetone!
If this isn't pure enough, a fractional still could be made by boring a hole (use a hot stone on the end of a stick, or a shell, through a large piece of bamboo. The ridges on each side would act as steps to condense the liquid on. No need to invent the iron age!
Answer: Get some decomposing vegetation, put it in a pig's bladder - wait.
"...acetone occurs naturally in the environment through decomposing vegetation..." https://badacetone.weebly.com/risks-and-benefits.html